Method and apparatus for determining precoding matrix indicator, user equipment, and base station

ABSTRACT

A precoding matrix indicator (PMI) is determined for a user equipment or a base station, where the PMI corresponds to a precoding matrix W, and the precoding matrix W satisfies a first condition, a second condition, or a third condition; and the PMI is sent to a base station. The precoding matrix indicator can effectively control a beam, especially a beam shape and a beam orientation, in a horizontal direction and a perpendicular direction.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/819,179, filed on Nov. 21, 2017, which is a continuation of U.S.application Ser. No. 15/463,966, filed on Mar. 20, 2017, now U.S. Pat.No. 9,843,370, which is a continuation of U.S. application Ser. No.14/982,286, filed on Dec. 29, 2015, now U.S. Pat. No. 9,634,748, whichis a continuation of International Application No. PCT/CN2013/078514,filed on Jun. 29, 2013. All of the afore-mentioned patent applicationsare hereby incorporated by reference in their entireties.

TECHNICAL FIELD

The present disclosure relates to data transmission technologies, and inparticular, to a method and an apparatus for determining a precodingmatrix indicator, user equipment, and a base station, and belongs to thefield of communications technologies.

BACKGROUND

By means of transmit precoding and receive combining, a multiple inputmultiple output (MIMO) system can obtain a diversity gain and an arraygain. A system using precoding may be represented as:y=HVs+n

where y is a received signal vector, H is a channel matrix, V is aprecoding matrix, s is a transmitted symbol vector, and n is aninterference and noise vector.

Optimal precoding usually requires that a transmitter completely knowschannel state information (CSI). A commonly-used method is: userequipment (User Equipment, UE for short) quantizes instantaneous CSI,and sends a feedback to a base station.

In an existing long term evolution (LTE) R8-R11 (Release 8-11) system,CSI fed back by UE includes rank indicator (RI) information, precodingmatrix indicator (PMI) information, channel quality indicator (CQI)information, and the like, where the RI and the PMI respectivelyindicate a quantity of used layers and a precoding matrix. A set of aused precoding matrix is generally referred to as a codebook, where eachprecoding matrix is a code word in the codebook.

In order to reduce system costs and meanwhile achieve higherrequirements on a system capacity and coverage, an active antenna system(AAS) has been widely studied. Compared with an existing base stationantenna that has only a capability of controlling a beam orientation ina horizontal direction, the can provide a capability of controlling abeam orientation both in a horizontal direction and in a perpendiculardirection, and meanwhile, has a capability of controlling a beam shapeto control power distribution in space. However, in the prior art, aprecoding matrix fed back by UE to a node device cannot effectivelycontrol a beam, especially a beam shape and a beam orientation, in ahorizontal direction and a perpendicular direction at the same time.

SUMMARY

Embodiments of the present invention provide a method and an apparatusfor determining a precoding matrix indicator, user equipment, and a basestation, which are used to effectively control a beam, especially a beamshape and a beam orientation, in a horizontal direction and aperpendicular direction.

A first aspect of the present invention provides a method fordetermining a precoding matrix indicator, including:

determining a precoding matrix indicator PMI, where the PMI correspondsto a precoding matrix W, and the precoding matrix W satisfies a firstcondition, a second condition, or a third condition; and

sending the PMI to a base station, where

the first condition is that the precoding matrix W satisfies W=DV, wherethe matrix D is a diagonal matrix, D=α·diag {u₁,u₂, . . .,u_(n),u_(n)*,u_(n−1)*, . . . ,u₁*}, α is complex factor, a complexnumber u_(i)* is a conjugate complex number of a complex number u_(i),and n is determined by a quantity of antenna ports; and the matrix V isa constant modulus matrix;

the second condition is that the precoding matrix W includes one or morecolumn vectors of a block diagonal matrix W₁, or the precoding matrix Wis obtained by performing weighted combination on one or more columnvectors of a block diagonal matrix W₁, where W₁=diag {X₁, . . . ,X_(N)_(B) }, and N_(B)≥1, where at least one block matrix X is a product X=DVof a matrix D and a matrix V, and X ∈ {X₁,X₂, . . . ,X_(N) _(B) }; thematrix D is a diagonal matrix, D=α·diag {u₁,u₂, . . .,u_(n),u_(n)*,u_(n−1)*,u₁*}, α is a complex factor, a complex numberu_(i)* is a conjugate complex number of a complex number u_(i), and n isdetermined by a quantity of antenna ports; and the matrix V is aconstant modulus matrix; and

the third condition is that the precoding matrix W includes one or morecolumn vectors of a block diagonal matrix W₁, or the precoding matrix Wis obtained by performing weighted combination on one or more columnvectors of a block diagonal matrix W₁, where W₁=diag {X₁, . . . ,X_(N)_(B) }, and N_(B)≥1, where at least one block matrix X is a Kroneckerproduct of a matrix A and a matrix B, X=A⊗B, and X ∈ {X₁,X₂, . . .,X_(N) _(B) }; the matrix A or the matrix B is a product of a matrix Dand a matrix V; the matrix D is a diagonal matrix, D=α·diag {u₁,u₂, . .. ,u_(n),u_(n)*,u_(n−1)*, . . . ,u₁*}, α is a complex factor, a complexnumber u_(i)* is a conjugate complex number of complex number u_(i),i=1, . . . ,n, and n is a quantity of rows of the matrix A or the matrixB; and the matrix V is a constant modulus matrix.

With reference to the foregoing first aspect, in a first possibleimplementation manner, in the second condition or the third condition,the precoding matrix w satisfies W=W₁W₂, where the matrix W₂ is used toselect one or more column vectors of the matrix W₁; or is used toperform weighted combination on one or more column vectors of the W₁ toobtain the precoding matrix W.

With reference to the foregoing first aspect or the first possibleimplementation manner of the first aspect, in a second possibleimplementation manner, phases of diagonal elements u₁,u₂, . . . ,u_(n)of matrix D form an arithmetic progression.

With reference to the foregoing first aspect or either possibleimplementation manner of the foregoing first aspect, in a third possibleimplementation manner, the matrix V includes a column vector 1 and/or atleast one column vector v, the column vector 1 is a column vector whoseelements are all 1, and the column vector v is v=[v₁ v₂ L v_(n) v _(n) v_(n−1) L v ₁]^(r), where an element is v _(i)=−v_(i)=±1, and i=1, . . .,n.

With reference to the third possible implementation manner of theforegoing first aspect, in a fourth possible implementation manner, thematrix V includes only the column vector 1 and the at least one columnvector v, and when the matrix V includes multiple column vectors v, themultiple column vectors v are different.

With reference to the third or fourth possible implementation manner ofthe foregoing first aspect, in a fifth possible implementation manner,the column vector v of the matrix V is a column vector of a matrix[H^(T) H^(T)]^(T), where a matrix H is a Hadamard matrix.

With reference to any possible implementation manner of the foregoingfirst aspect, in a sixth possible implementation manner, the PMIincludes a first index PMI1 and a second index PMI2, where

when the precoding matrix W satisfies the first condition, the firstindex PMI1 corresponds to the matrix D, and the second index PMI2corresponds to the matrix V;

when the precoding matrix W satisfies the second condition, the firstindex PMI1 corresponds to the matrix W₁, and the second index PMI2corresponds to the matrix W₂; or

when the precoding matrix W satisfies the third condition, the firstindex PMI1 corresponds to the matrix W₁, and the second index PMI2corresponds to the matrix W₂.

With reference to the sixth possible implementation manner of theforegoing first aspect, in a seventh possible implementation manner, thefirst index PMI1 and the second index PMI2 have different time-domaingranularities or frequency-domain granularities; or the first index PMI1and the second index PMI2 are sent to the base station by usingdifferent time periods.

With reference to the foregoing first aspect or any possibleimplementation manner of the first aspect, in an eighth possibleimplementation manner, the method further includes:

receiving a reference signal sent by the base station; and

selecting, from a codebook according to the reference signal, theprecoding matrix W corresponding to the PMI.

With reference to the eighth possible implementation manner of the firstaspect, the codebook includes a precoding matrix W_(i) and a precodingmatrix W_(j), and the two precoding matrices satisfy W_(i)=D(i,j)W_(j),where D(i,j)=α_((i,j))diag {μ₁,μ₂, . . . μ_(n),μ_(n)*,μ_(n−1)*, . . .,μ₁*}, α_((i,j)) is a complex factor, a complex number μ_(m)* is aconjugate complex number of a complex number μ_(m), m=1, . . . ,n, and nis determined by a quantity of antenna ports.

With reference to the ninth possible implementation manner of the firstaspect, in a tenth possible implementation manner, phases of diagonalelements μ₁, μ₂, . . . ,μ_(n) of the matrix D(i,j) form an arithmeticprogression.

With reference to the eighth possible implementation manner of the firstaspect, the codebook includes a precoding matrix W_(i) and a precodingmatrix W_(k), and the two precoding matrices satisfy D_(i) ⁻¹W_(i)=D_(k)⁻¹W_(k)=V, where D_(m)=α_(m)·diag {u_(m,1),u_(m,2), . . .,u_(m,n),u_(m,n−1)*, . . . ,u_(m,1)*}, m=i,k, α_(m) is a complex factor,a complex number u_(m,l)* is a conjugate complex number of a complexnumber u_(m,l), m=i,k, l=1, . . . ,n, and n is determined by a quantityof antenna ports.

With reference to the eleventh possible implementation manner of thefirst aspect, in a twelfth possible implementation manner, phases ofdiagonal elements u_(m,1),u_(m,2), . . . ,u_(m,n) of the matrix D_(m)form an arithmetic progression.

A second aspect of the present invention provides a method fordetermining a precoding matrix indicator, including:

receiving a precoding matrix indicator PMI sent by user equipment; and

determining a corresponding precoding matrix W according to the PMI,where the precoding matrix W satisfies a first condition, a secondcondition, or a third condition, where

the first condition is that the precoding matrix W satisfies W=DV;

the second condition is that the precoding matrix W includes one or morecolumn vectors of a block diagonal matrix W₁, or the precoding matrix Wis obtained by performing weighted combination on one or more columnvectors of a block diagonal matrix W₁, where W₁=diag {X₁, . . . ,X_(N)_(B) }, and N_(B)≥1, where at least one block matrix X is a product X=DVof a matrix D and a matrix V, and X ∈ {X₁,X₂, . . . ,X_(N) _(B) }; and

the third condition is that the precoding matrix W includes one or morecolumn vectors of a block diagonal matrix W₁ or the precoding matrix Wis obtained by performing weighted combination on one or more columnvectors of a block diagonal matrix W₁, where W₁=diag {X₁, . . . X_(N)_(B) }, and N_(B)≥1 where at least one block matrix X is a Kroneckerproduct of a matrix A and a matrix B, X=A⊗B, and X ∈ {X₁,X₂, . . .,X_(N) _(B) }; the matrix A or the matrix B is a product of a matrix Dand a matrix V; the matrix D is a diagonal matrix, i=1, . . . ,n, and nis a quantity of rows of the matrix A or the matrix B, where

the matrix D is a diagonal matrix, D=α·diag {u₁,u₂, . . . ,u_(n),u_(n)*,u_(n−1)*, . . . ,u₁*}, α is a complex factor, a complex numberu_(i)* is a conjugate complex number of a complex number u_(i), and n isdetermined by a quantity of antenna ports; and the matrix V is aconstant modulus matrix.

With reference to the second aspect, in a first possible implementationmanner, in the second condition or the third condition, the precodingmatrix W satisfies W=W₁W₂, where the matrix W₂ is used to select one ormore column vectors of the matrix W₁; or is used to perform weightedcombination on one or more column vectors of the W₁ to obtain theprecoding matrix W.

With reference to the second aspect or the first possible implementationmanner of the second aspect, in a second possible implementation manner,phases of diagonal elements u₁,u₂, . . . ,u_(n) of the matrix D form anarithmetic progression.

With reference to the second aspect or either possible implementationmanner of the second aspect, in a third possible implementation manner,the matrix V includes a column vector 1 and/or at least one columnvector v, the column vector 1 is a column vector whose elements are all1, and the column vector v is v=[v₁ v₂ L v_(n) v _(n) v _(n−1) L v₁]^(T)where an element is v _(i)=−v_(i),v_(i)=±1, and i=1, . . . ,n.

With reference to the third possible implementation manner of theforegoing second aspect, in a fourth possible implementation manner, thematrix V includes only the column vector 1 and the at least one columnvector v, and when the matrix V includes multiple column vectors v, themultiple column vectors v are different.

With reference to the third or fourth possible implementation manner ofthe foregoing second aspect, in a fifth possible implementation manner,the column vector v of the matrix V is a column vector of a matrix[H^(T) H^(T)]^(T), where a matrix H is a Hadamard matrix.

With reference to any possible implementation manner of the foregoingsecond aspect, in a sixth possible implementation manner, the precodingmatrix indicator PMI includes a first index PMI1 and a second indexPMI2, where

when the precoding matrix W satisfies the first condition, the firstindex PMI1 corresponds to the matrix D, and the second index PMI2corresponds to the matrix V;

when the precoding matrix W satisfies the second condition the firstindex PMI1 corresponds to the matrix W₁, and the second index PMI2corresponds to the matrix W₂; or

when the precoding matrix W satisfies the third condition, the firstindex PMI1 corresponds to the matrix W₁, and the second index PMI2corresponds to the matrix W₂.

With reference to the sixth possible implementation manner of theforegoing second aspect, in a seventh possible implementation manner,the first index PMI1 and the second index PMI2 have differenttime-domain granularities or frequency-domain granularities; or thefirst index PMI1 and the second index PMI2 are sent to a base station byusing different time periods.

With reference to the foregoing second aspect or any possibleimplementation manner of the second aspect, in an eighth possibleimplementation manner, the determining a corresponding precoding matrixW according to the PMI includes:

selecting the corresponding precoding matrix W from a codebook accordingto the PMI.

With reference to the eighth possible implementation manner of thesecond aspect, the codebook includes a precoding matrix W_(i) and aprecoding matrix W_(j), and the two precoding matrices satisfyW_(i)=D(i,j)W_(j), where D(i,j)=α_((i,j))diag {μ₁,μ₂, . . .,μ_(n),μ_(n)*,μ_(n−1)*, . . . ,μ₁*}, α_((i,j)) is a complex factor, acomplex number μ_(m)* is a conjugate complex number of a complex numberμ_(m), m=1, . . . ,n and n is determined by a quantity of antenna ports.

With reference to the eighth possible implementation manner of thesecond aspect, in a tenth possible implementation manner, phases ofdiagonal elements μ₁,μ₂, . . . ,μ_(n) of the matrix D(i,j) form anarithmetic progression.

With reference to the second aspect, in an eleventh possibleimplementation manner, the codebook includes a precoding matrix W_(i)and a precoding matrix W_(k), and the two precoding matrices satisfyD_(i) ⁻¹W_(i)=D_(k) ⁻¹W_(k)=V, where D_(m)=α_(m)·diag {u_(m,1),u_(m,2),. . . ,u_(m,n)u_(m,n)*,u_(m,n−1)*, . . . ,u_(m,1)*}, m=i,k, α_(m) is acomplex factor, a complex number u_(m,l)* is a conjugate complex numberof a complex number u_(m,l), m=i,k, l=1, . . . ,n, and n is determinedby a quantity of antenna ports.

With reference to the eleventh possible implementation manner of thesecond aspect, in a twelfth possible implementation manner, phases ofdiagonal elements u_(m,1),u_(m,2), . . . ,u_(m,n) of the matrix D_(m)form an arithmetic progression.

A third aspect of the present invention provides a method fordetermining a precoding matrix indicator, including:

determining a first precoding matrix indicator PMI, where the PMIcorresponds to a precoding matrix W_(i) in a codebook; and

sending the first PMI to a base station, where

the codebook includes at least: the precoding matrix W_(i) and aprecoding matrix W_(j), and the precoding matrix W_(i) and the precodingmatrix W_(j) in the codebook satisfy W_(i)=D(i,j)W_(j), whereD(i,j)=α_((i,j))diag {μ₁,μ₂, . . . ,μ_(n),μ_(n)*,μ_(n−1)*, . . . ,μ₁*},α_((i,j)) is a complex factor, a complex number μ_(m)* is a conjugatecomplex number of a complex number μ_(m), m=1, . . . ,n, and n isdetermined by a quantity of antenna ports.

With reference to the third aspect, in a first possible implementationmanner, phases of diagonal elements μ₁, μ₂, . . . ,μ_(n) the matrixD(i,j) form an arithmetic progression.

A fourth aspect of the present invention provides a method fordetermining a precoding matrix indicator, including:

receiving a first precoding matrix indicator PMI sent by user equipment;and

determining a corresponding precoding matrix W_(i) from a codebookaccording to the first PMI, where

the codebook includes at least: the precoding matrix W_(i) and aprecoding matrix W_(j), and the precoding matrix W_(i) and the precodingmatrix W_(j) in the codebook satisfy W_(i)=D(i,j)W_(j), whereD(i,j)=α_((i,j))diag {μ₁,μ₂, . . . , μ_(n),μ_(n)*, μ_(n−1)*, . . .,μ₁*}, α_((i,j)) is a complex factor, a complex number μ_(m)* is aconjugate complex number of a complex number μ_(m), m=1, . . . ,n, and nis determined by a quantity of antenna ports.

With reference to the fourth aspect, in a first possible implementationmanner, phases of diagonal elements μ₁,μ₂, . . . ,μ_(n) of the matrixD(i,j) form an arithmetic progression.

A fifth aspect of the present invention provides a method fordetermining a precoding matrix indicator, including:

determining a first precoding matrix indicator PMI, where the first PMIcorresponds to a precoding matrix W_(i) in a codebook; and

sending the first PMI to a base station, where

the codebook includes at least: the precoding matrix W_(i) and aprecoding matrix W_(j), and the precoding matrix W_(i) and a precodingmatrix W_(k) in the codebook satisfy D_(i) ⁻¹W_(i)=D_(k) ⁻¹W_(k)=V,where D_(m)=α_(m)·diag {u_(m,1), u_(m,2), . . . ,u_(m,n), u_(m,n)*,u_(m,n−1)*, . . . ,u_(m,1)*}, m=i,k, α_(m) is a complex factor, acomplex number u_(m,l)* is a conjugate complex number of a complexnumber u_(m,l), m=i,k, l=1, . . . ,n, is determined by a quantity ofantenna ports, and the matrix V is a constant modulus matrix.

With reference to the fifth aspect, in a first possible implementationmanner, phases of diagonal elements u_(m,1),u_(m,2), . . . ,u_(m,n) ofthe matrix D_(m) form an arithmetic progression.

A sixth aspect of the present invention provides a method fordetermining a precoding matrix indicator, including:

receiving a first precoding matrix indicator PMI sent by user equipment;and

determining a corresponding precoding matrix W_(i) from a codebookaccording to the first PMI, where

the codebook includes at least: the precoding matrix W_(i) and aprecoding matrix W_(j), and the precoding matrix W_(i) and a precodingmatrix W_(k) in the codebook satisfy D_(i) ⁻¹W_(i)=D_(k) ⁻¹W_(k)=V,where D_(m)=α_(m)·diag {u_(m,1),u_(m,2), . . .,u_(m,n),u_(m,n)*,u_(m,n−1)*, . . . ,u_(m,1)*}, m=i,k, α_(m) is acomplex factor, a complex number u_(m,l)* is a conjugate complex numberof a complex number u_(m,l), m=i,k, l=1, . . . ,n, n is determined by aquantity of antenna ports, and the matrix V is a constant modulusmatrix.

With reference to the sixth aspect, in a first possible implementationmanner, phases of diagonal elements u_(m,1),u_(m,2), . . . ,u_(m,n) ofthe matrix D_(m) form an arithmetic progression.

A seventh aspect of the present invention provides an apparatus fordetermining a precoding matrix indicator, including:

a first determining module, configured to determine a precoding matrixindicator PMI, where the PMI corresponds to a precoding matrix W, andthe precoding matrix W satisfies a first condition, a second condition,or a third condition; and

a first sending module, configured to send the PMI to a base station,where

the first condition is that the precoding matrix W satisfies W=DV, wherethe matrix D is a diagonal matrix, D=α·diag {u₁,u₂, . . .,u_(m),u_(n)*,u_(n−1)*, . . . , u₁*}, α is a complex factor, a complexnumber u_(i)* is a conjugate complex number of a complex number u_(i),and n is determined by a quantity of antenna ports; and the matrix V isa constant modulus matrix;

the second condition is that the precoding matrix W includes one or morecolumn vectors of a block diagonal matrix W₁, or the precoding matrix Wis obtained by performing weighted combination on one or more columnvectors of a block diagonal matrix W₁, where W₁=diag {X₁, . . . ,X_(N)_(B) }, and N_(B)≥1, where at least one block matrix X is a product X=DVof a matrix D and a matrix V, and X ∈ {X₁,X₂, . . . ,X_(N) _(B) }; thematrix D is a diagonal matrix, D=α·diag {u₁,u₂, . . .,u_(n),u_(n)*,u_(n−1)*, . . . ,u₁*}, α is a complex factor, a complexnumber u_(i)* is a conjugate complex number of a complex number u_(i),and n is determined by a quantity of antenna ports; and the matrix V isa constant modulus matrix; and

the third condition is that the precoding matrix W includes one or morecolumn vectors of a block diagonal matrix W₁, or the precoding matrix Wis obtained by performing weighted combination on one or more columnvectors of a block diagonal matrix W₁, where W₁=diag {X₁, . . . ,X_(N)_(B) }, and N_(B)≥1, where at least one block matrix X is a Kroneckerproduct of a matrix A and a matrix B, X=A⊗B, and X ∈ {X₁,X₂, . . .,X_(N) _(B) }; the matrix A or the matrix B is a product of a matrix Dand a matrix V; the matrix D is a diagonal matrix, D=α·diag {u₁,u₂, . .. ,u_(n),u_(n)*,u_(n−1)*, . . . ,u₁*}, α is a complex factor, a complexnumber u_(i)* is a conjugate complex number of a complex number u_(i),i=1, . . . ,n, and n is a quantity of rows of the matrix A or the matrixB; and the matrix V is a constant modulus matrix.

With reference to the foregoing seventh aspect, in a first possibleimplementation manner, in the second condition or the third condition,the precoding matrix W satisfies W=W₁W₂, where the matrix W₂ is used toselect one or more column vectors of the matrix W₁; or is used toperform weighted combination on one or more column vectors of the W₁ toobtain the precoding matrix W.

With reference to the foregoing seventh aspect or the first possibleimplementation manner of the seventh aspect, in a second possibleimplementation manner, phases of diagonal elements u₁,u₂, . . . ,u_(n)of the matrix D form an arithmetic progression.

With reference to the foregoing seventh aspect or either possibleimplementation manner of the foregoing seventh aspect, in a thirdpossible implementation manner, the matrix V includes a column vector 1and/or at least one column vector v, the column vector 1 is a columnvector whose elements are all 1, and the column vector v is v=[v₁ v₂ Lv_(n) v _(n) v _(n−1) L v ₁]^(T), where the an element is v_(i)=−v_(i),v_(i)=±1, and i=1, . . . ,n.

With reference to the third possible implementation manner of theforegoing seventh aspect, in a fourth possible implementation manner,the matrix V includes only the column vector 1 and the at least onecolumn vector v, and when the matrix V includes multiple column vectorsv, the multiple column vectors v are different.

With reference to the third or fourth possible implementation manner ofthe foregoing seventh aspect, in a fifth possible implementation manner,the column vector v of the matrix V is a column vector of a matrix[H^(T) H^(T)]^(T), where a matrix H is a Hadamard matrix.

With reference to any possible implementation manner of the foregoingseventh aspect, in a sixth possible implementation manner, the PMIincludes a first index PMI1 and a second index PMI2, where

when the precoding matrix W satisfies the first condition, the firstindex PMI1 corresponds to the matrix D, and the second index PMI2corresponds to the matrix V;

when the precoding matrix W satisfies the second condition, the firstindex PMI1 corresponds to the matrix W₁, and the second index PMI2corresponds to the matrix W₂; or

when the precoding matrix W satisfies the third condition, the firstindex PMI1 corresponds to the matrix W₁, and the second index PMI2corresponds to the matrix W₂.

With reference to the sixth possible implementation manner of theforegoing seventh aspect, in a seventh possible implementation manner,the first index PMI1 and the second index PMI2 have differenttime-domain granularities or frequency-domain granularities; or thefirst index PMI1 and the second index PMI2 are sent to the base stationby using different time periods.

With reference to the foregoing seventh aspect or any possibleimplementation manner of the seventh aspect, in an eighth possibleimplementation manner, the apparatus further includes:

a first receiving module, configured to receive a reference signal sentby the base station, and select, from a codebook according to thereference signal, the precoding matrix W corresponding to the PMI.

With reference to the eighth possible implementation manner of theseventh aspect, the codebook includes a precoding matrix W_(i) and aprecoding matrix W_(i), and the two precoding matrices satisfyW_(i)=D(i,j)W_(j), where D(i,j)=α_((i,j))diag {μ₁,μ₂, . . .,μ_(n),μ_(n)*,μ_(n−1)*, . . . ,μ₁*}, α_((i,j)) is a complex factor, acomplex number μ_(m)* is a conjugate complex number of a complex numberμ_(m), m=1, . . . , n, and n is determined by a quantity of antennaports.

With reference to the ninth possible implementation manner of theseventh aspect, in a tenth possible implementation manner, phases ofdiagonal elements μ₁,μ₂, . . . ,μ_(n) of the matrix D(i,j) form anarithmetic progression.

With reference to the eighth possible implementation manner of theseventh aspect, the codebook includes a precoding matrix W_(i) and aprecoding matrix W_(k), and the two precoding matrices satisfy D_(i)⁻¹W_(i)D_(k) ⁻¹W_(k)=V, where D_(m)=α_(m)·diag {u_(m,1),u_(m,2), . . .,u_(m,n),u_(m,n)*,u_(m,n−1)*, . . . ,u_(m,1)*}, m=i,k, α_(m) is acomplex factor, a complex number μ_(m,l)* is a conjugate complex numberof a complex number μ_(m,l), m=i,k, l=1, . . . ,n, and n is determinedby a quantity of antenna ports.

With reference to the eleventh possible implementation manner of theseventh aspect, in a twelfth possible implementation manner, phases ofdiagonal elements u_(m,1),u_(m,2), . . . ,u_(m,n) of the matrix D_(m)form an arithmetic progression.

An eighth aspect of the present invention provides an apparatus fordetermining a precoding matrix indicator, including:

a second receiving module, configured to receive a precoding matrixindicator PMI sent by user equipment; and

a second determining module, configured to determine a correspondingprecoding matrix W according to the PMI, where the precoding matrix Wsatisfies a first condition, a second condition, or a third condition,where

the first condition is that the precoding matrix W satisfies W=DV;

the second condition is that the precoding matrix W includes one or morecolumn vectors of a block diagonal matrix W₁, or the precoding matrix Wis obtained by performing weighted combination on one or more columnvectors of a block diagonal matrix W₁, where W₁=diag {X₁, . . . ,X_(N)_(B) }, and N_(B)≥1, where at least one block matrix X is a product X=DVof a matrix D and a matrix V, and X ∈ {X₁,X₂, . . . ,X_(N) _(B) }; and

the third condition is that the precoding matrix W includes one or morecolumn vectors of a block diagonal matrix W₁, or the precoding matrix Wis obtained by performing weighted combination on one or more columnvectors of a block diagonal matrix W₁, where W₁=diag {X₁, . . . ,X_(N)_(B) }, and N_(B)≥1, where at least one block matrix X is a Kroneckerproduct of a matrix A and a matrix B, X=A⊗B, and X ∈ {X₁,X₂, . . .,X_(N) _(B) }; the matrix A or the matrix B is a product of a matrix Dand a matrix V; the matrix D is a diagonal matrix, i=1, . . . ,n, and nis a quantity of rows of the matrix A or the matrix B, where

the matrix D is a diagonal matrix, D=α·diag {u₁,u₂, . . .,u_(n),u_(n)*,u_(n−1)*, . . . ,u₁*}, α is a complex factor, a complexnumber u_(i)* is a conjugate complex number of a complex number u_(i),and n is determined by a quantity of antenna ports; and the matrix V isa constant modulus matrix.

With reference to the eighth aspect, in a first possible implementationmanner, in the second condition or the third condition, the precodingmatrix W satisfies W=W₁W₂, where the matrix W₂ is used to select one ormore column vectors of the matrix W₁; or is used to perform weightedcombination on one or more column vectors of the W₁ to obtain theprecoding matrix W.

With reference to the eighth aspect or the first possible implementationmanner of the eighth aspect, in a second possible implementation manner,phases of diagonal elements u₁,u₂, . . . ,u_(n) of the matrix D form anarithmetic progression.

With reference to the eighth aspect or either possible implementationmanner of the eighth aspect, in a third possible implementation manner,the matrix V includes a column vector 1 and/or at least one columnvector V, the column vector 1 is a column vector whose elements are all1, and the column vector v is v=[v₁ v₂ L v_(n) v _(n) v _(n−1) L v_(j)]^(T), where an element is v _(i)=−v_(i),v_(i)=±1, and i=1, . . .,n.

With reference to the third possible implementation manner of theforegoing eighth aspect, in a fourth possible implementation manner, thematrix V includes only the column vector 1 and the at least one columnvector v, and when the matrix V includes multiple column vectors v, themultiple column vectors v are different.

With reference to the third or fourth possible implementation manner ofthe foregoing eighth aspect, in a fifth possible implementation manner,the column vector v of the matrix V is a column vector of a matrix[H^(T) H^(T)]^(T), where a matrix H is a Hadamard matrix.

With reference to any possible implementation manner of the foregoingeighth aspect, in a sixth possible implementation manner, the precodingmatrix indicator PMI includes a first index PMI1 and a second indexPMI2, where

when the precoding matrix W satisfies the first condition, the firstindex PMI1 corresponds to the matrix D, and the second index PMI2corresponds to the matrix V;

when the precoding matrix W satisfies the second condition, the firstindex PMI1 corresponds to the matrix W₁, and the second index PMI2corresponds to the matrix W₂; or

when the precoding matrix W satisfies the third condition, the firstindex PMI1 corresponds to the matrix W₁, and the second index PMI2corresponds to the matrix W₂.

With reference to the sixth possible implementation manner of theforegoing eighth aspect, in a seventh possible implementation manner,the first index PMI1 and the second index PMI2 have differenttime-domain granularities or frequency-domain granularities; or thefirst index PMI1 and the second index PMI2 are sent to a base station byusing different time periods.

With reference to the foregoing eighth aspect or any possibleimplementation manner of the eighth aspect, in an eighth possibleimplementation manner, the determining a corresponding precoding matrixW according to the PMI includes:

selecting the corresponding precoding matrix W from a codebook accordingto the PMI.

With reference to the eighth possible implementation manner of theeighth aspect, in a ninth possible implementation manner, the codebookincludes a precoding matrix W_(i) and a precoding matrix W_(j), and thetwo precoding matrices satisfy W_(i)=D(i,j)W_(j), whereD(i,j)=α_((i,j))diag {μ₁,μ₂, . . . ,μ_(n),μ_(n)*,μ_(n−1)*, . . . ,μ₁*},α_((i,j)) is a complex factor, a complex number μ_(m)* is a conjugatecomplex number of a complex number μ_(m), m=1, . . . ,n, and n isdetermined by a quantity of antenna ports.

With reference to the ninth possible implementation manner of the eighthaspect, in a tenth possible implementation manner, phases of diagonalelements μ₁,μ₂, . . . ,μ_(n) of the matrix D(i,j) form an arithmeticprogression.

With reference to the eighth possible implementation manner of theeighth aspect, the codebook includes a precoding matrix W_(i) and aprecoding matrix W_(k), and the two precoding matrices satisfy D_(i)⁻¹W_(i)=D_(k) ⁻¹W_(k)=V, where D_(m)=α_(m)·diag {u_(m,1),u_(m,2), . . .,u_(m,n),u_(m,n)*,u_(m,n−1)*, . . . ,u_(m,1)*}, m=i,k, α_(m) is acomplex factor, a complex number u_(m,l)* is a conjugate complex numberof a complex number u_(m,l), m=i,k, l=1, . . . ,n, and n is determinedby a quantity of antenna ports.

With reference to the eleventh possible implementation manner of theeighth aspect, in a twelfth possible implementation manner, phases ofdiagonal elements u_(m,1),u_(m,2), . . . ,u_(m,n) of the matrix D_(m)form an arithmetic progression.

A ninth aspect of the present invention provides an apparatus fordetermining a precoding matrix indicator, including:

a third determining module, configured to determine a first precodingmatrix indicator PMI, where the PMI corresponds to a precoding matrixW_(i) in a codebook; and

a second sending module, configured to send the first PMI to a basestation, where

the codebook includes at least: the precoding matrix W_(i) and aprecoding matrix W_(j), and the precoding matrix W_(i) and the precodingmatrix W_(j) in the codebook satisfy W_(i)=D(i,j)W_(j), whereD(i,j)=α_((i,j))diag {μ₁,μ₂, . . . ,μ_(n),μ_(n)*,μ_(n−1)*, . . . ,μ₁*},α_((i,j)) is a complex factor, a complex number μ_(m)* is a conjugatecomplex number of a complex number μ_(m), m=1, . . . ,n, and n isdetermined by a quantity of antenna ports.

With reference to the ninth aspect, in a first possible implementationmanner, phases of diagonal elements μ₁, μ₂, . . . ,μ_(n) of the matrixD(i,j) form an arithmetic progression.

A tenth aspect of the present invention provides an apparatus fordetermining a precoding matrix indicator, including:

a third receiving module, configured to receive a first precoding matrixindicator PMI sent by user equipment; and

a fourth determining module, configured to determine a correspondingprecoding matrix W_(i) from a codebook according to the first PMI, where

the codebook includes at least: the precoding matrix W_(i) and aprecoding matrix W_(j), and the precoding matrix W_(i) and the precodingmatrix W_(j) in the codebook satisfy W_(i)=D(i,j)W_(j), whereD(i,j)=α_((i,j))diag {μ₁,μ₂, . . . ,μ_(n),μ_(n)*,μ_(n−1)*, . . . ,μ₁*},α_((i,j)) is a complex factor, a complex number μ_(m)* is a conjugatecomplex number of a complex number μ_(m), m=1, . . . ,n, and n isdetermined by a quantity of antenna ports.

With reference to the tenth aspect, in a first possible implementationmanner, phases of diagonal elements μ₁,μ₂, . . . ,μ_(n) of the matrixD(i,j) form an arithmetic progression.

An eleventh aspect of the present invention provides an apparatus fordetermining a precoding matrix indicator, including:

a fifth determining module, configured to determine a first precodingmatrix indicator PMI, where the first PMI corresponds to a precodingmatrix W_(i) in a codebook; and

a third sending module, configured to send the first PMI to a basestation, where

the codebook includes at least: the precoding matrix W_(i) and aprecoding matrix W_(j), and the precoding matrix W_(i) and a precodingmatrix W_(k) in the codebook satisfy D_(i) ⁻¹W_(i)=D_(k) ⁻¹W_(k)=V,where D_(m)=α_(m)·diag {u_(m,1),u_(m,2), . . .,u_(m,n)u_(m,n)*,u_(m,n−1)*, . . . ,u_(m,1)*}, m=i,k, α_(m) is a complexfactor, a complex number u_(m,l)* is a conjugate complex number of acomplex number u_(m,l), m=i,k, l=1, . . . ,n, n is determined by aquantity of antenna ports, and the matrix V is a constant modulusmatrix.

With reference to the eleventh aspect, in a first possibleimplementation manner, phases of diagonal elements u_(m,1),u_(m,2), . .. ,u_(m,n) of the matrix D_(m) form an arithmetic progression.

A twelfth aspect of the present invention provides an apparatus fordetermining a precoding matrix indicator, including:

a fourth receiving module, configured to receive a first precodingmatrix indicator PMI sent by user equipment; and

a sixth determining module, configured to determine a correspondingprecoding matrix W_(i) from a codebook according to the first PMI, where

the codebook includes at least: the precoding matrix W_(i) and aprecoding matrix W_(i), and the precoding matrix W_(i) and a precodingmatrix W_(k) in the codebook satisfy D_(i) ⁻¹W_(i)=D_(k) ⁻¹W_(k)=V,where D_(m)=α_(m)·diag {u_(m,1),u_(m,2), . . .,u_(m,n),u_(m,n)*,u_(m,n−1)*, . . . ,u_(m,1)*}, m=i,k, α_(m) is acomplex factor, a complex number u_(m,l)* is a conjugate complex numberof a complex number u_(m,l), m=i,k, l=1, . . . ,n, n is determined by aquantity of antenna ports, and the matrix V is a constant modulusmatrix.

With reference to the twelfth aspect, in a first possible implementationmanner, phases of diagonal elements u_(m,1),u_(m,2), . . . ,u_(m,n) ofthe matrix D_(m) form an arithmetic progression.

A thirteenth aspect of the present invention provides user equipment,including:

a first processor, configured to determine a precoding matrix indicatorPMI, where the PMI corresponds to a precoding matrix W, and theprecoding matrix W satisfies a first condition, a second condition, or athird condition; and

a first transmitter, configured to send the PMI to a base station, where

the first condition is that the precoding matrix W satisfies W=DV, wherethe matrix D is a diagonal matrix, D=α·diag {u₁,u₂, . . .,u_(n),u_(n)*,u_(n−1)*, . . . ,u₁*}, α is a complex factor, a complexnumber u_(i)* is a conjugate complex number of a complex number u_(i),and n is determined by a quantity of antenna ports; and the matrix V isa constant modulus matrix;

the second condition is that the precoding matrix W includes one or morecolumn vectors of a block diagonal matrix W₁, or the precoding matrix Wis obtained by performing weighted combination on one or more columnvectors of a block diagonal matrix W₁, where W₁=diag {X₁, . . . ,X_(N)_(B) }, and N_(B)≥1, where at least one block matrix X is a product X=DVof a matrix D and a matrix V, and X ∈ {X₁,X₂, . . . ,X_(N) _(B) }; thematrix D is a diagonal matrix, D=α·diag {u₁,u₂, . . .,u_(n),u_(n)*,u_(n−1)*, . . . ,u₁*}, α is a complex factor, a complexnumber u_(i)* is a conjugate complex number of a complex number u_(i),and n is determined by a quantity of antenna ports; and the matrix V isa constant modulus matrix; and

the third condition is that the precoding matrix W includes one or morecolumn vectors of a block diagonal matrix W₁, or the precoding matrix Wis obtained by performing weighted combination on one or more columnvectors of a block diagonal matrix W₁, where W₁=diag {X₁, . . . ,X_(N)_(B) }, and N_(B)≥1, where at least one block matrix X is a Kroneckerproduct of a matrix A and a matrix B, X=A⊗B, and X ∈ {X₁,X₂, . . .,X_(N) _(B) }; the matrix A or the matrix B is a product of a matrix Dand a matrix V; the matrix D is a diagonal matrix, D=α·diag {u₁,u₂, . .. ,u_(n),u_(n)*,u_(n−1)*, . . . ,u₁*}, α is a complex factor, a complexnumber u_(i)* is a conjugate complex number of a complex number u_(i),i=1, . . . ,n, and n is a quantity of rows of the matrix A or the matrixB; and the matrix V is a constant modulus matrix.

With reference to the foregoing thirteenth aspect, in a first possibleimplementation manner, in the second condition or the third condition,the precoding matrix W satisfies W=W₁W₂, where the matrix W₂ is used toselect one or more column vectors of the matrix W₁; or is used toperform weighted combination on one or more column vectors of the W₁ toobtain the precoding matrix W.

With reference to the foregoing thirteenth aspect or the first possibleimplementation manner of the thirteenth aspect, in a second possibleimplementation manner, phases of diagonal elements u₁,u₂, . . . ,u_(n)of the matrix D form an arithmetic progression.

With reference to the foregoing thirteenth aspect or either possibleimplementation manner of the foregoing thirteenth aspect, in a thirdpossible implementation manner, the matrix V includes a column vector 1and/or at least one column vector v, the column vector 1 is a columnvector whose elements are all 1, and the column vector v is v=[v₁ v₂ Lv_(n) v _(n) v _(n−1) L v ₁]^(T), where an element is v_(i)=−v_(i),v_(i)=±1, and i=1, . . . ,n.

With reference to the third possible implementation manner of theforegoing thirteenth aspect, in a fourth possible implementation manner,the matrix V includes only the column vector 1 and the at least onecolumn vector v, and when the matrix V includes multiple column vectorsv, the multiple column vectors v are different.

With reference to the third or fourth possible implementation manner ofthe foregoing thirteenth aspect, in a fifth possible implementationmanner, the column vector v of the matrix V is a column vector of amatrix [H^(T) H^(T)]^(T), where a matrix H is a Hadamard matrix.

With reference to any possible implementation manner of the foregoingthirteenth aspect, in a sixth possible implementation manner, the PMIincludes a first index PMI1 and a second index PMI2, where

when the precoding matrix W satisfies the first condition, the firstindex PMI1 corresponds to the matrix D, and the second index PMI2corresponds to the matrix V;

when the precoding matrix W satisfies the second condition, the firstindex PMI1 corresponds to the matrix W₁, and the second index PMI2corresponds to the matrix W₂; or

when the precoding matrix W satisfies the third condition, the firstindex PMI1 corresponds to the matrix W₁, and the second index PMI2corresponds to the matrix W₂.

With reference to the sixth possible implementation manner of theforegoing thirteenth aspect, in a seventh possible implementationmanner, the first index PMI1 and the second index PMI2 have differenttime-domain granularities or frequency-domain granularities; or thefirst index PMI1 and the second index PMI2 are sent to the base stationby using different time periods.

With reference to the foregoing thirteenth aspect or any possibleimplementation manner of the thirteenth aspect, in an eighth possibleimplementation manner, the user equipment further includes:

a first receiver, configured to receive a reference signal sent by thebase station, and select, from a codebook according to the referencesignal, the precoding matrix W corresponding to the PMI.

With reference to the eighth possible implementation manner of thethirteenth aspect, the codebook includes a precoding matrix W_(i) and aprecoding matrix W_(j), and the two precoding matrices satisfyW_(i)=D(i,j)W_(j), where D(i,j)=α_((i,j))diag {μ₁,μ₂, . . .,μ_(n),μ_(n)*,μ_(n−1)*, . . . ,μ₁*}, α_((i,j)) is a complex factor, acomplex number μ_(m)* is a conjugate complex number of a complex numberμ_(m), m=1, . . . ,n, and n is determined by a quantity of antennaports.

With reference to the ninth possible implementation manner of thethirteenth aspect, in a tenth possible implementation manner, phases ofdiagonal elements μ₁,μ₂, . . . ,μ_(n) of the matrix D(i,j) form marithmetic progression.

With reference to the eighth possible implementation manner of thethirteenth aspect, the codebook includes a precoding matrix W_(i) and aprecoding matrix W_(k), and the two precoding matrices satisfy D_(i)⁻¹W_(i)=D_(k) ⁻¹W_(k)=V, where D_(m)=α_(m)·diag {u_(m,1),u_(m,2), . . .,u_(m,n),u_(m,n)*,u_(m,n−1)*, . . . ,u_(m,1)*}, m=i,k, α_(m) is acomplex factor, a complex number u_(m,l)* is a conjugate complex numberof a complex number u_(m,l), m=i,k, l=1, . . . ,n, and n is determinedby a quantity of antenna ports.

With reference to the eleventh possible implementation manner of thethirteenth aspect, in a twelfth possible implementation manner, phasesof diagonal elements u_(m,1),u_(m,2), . . . ,u_(m,n) of the matrix D_(m)form an arithmetic progression.

A fourteenth aspect of the present invention provides a base station,including:

a second receiver, configured to receive a precoding matrix indicatorPMI sent by user equipment; and

a second processor, configured to: determine a corresponding precodingmatrix W according to the PMI, where the precoding matrix W satisfies afirst condition, a second condition, or a third condition, where

the first condition is that the precoding matrix W satisfies W=DV;

the second condition is that the precoding matrix W includes one or morecolumn vectors of a block diagonal matrix W₁, or the precoding matrix Wis obtained by performing weighted combination on one or more columnvectors of a block diagonal matrix W₁, where W₁=diag {X₁, . . . ,X_(N)_(B) }, and N_(B)≥1, where at least one block matrix X is a product X=DVof a matrix D and a matrix V, and X ∈ {X₁,X₂, . . . ,X_(N) _(B) }; and

the third condition is that the precoding matrix W includes one or morecolumn vectors of a block diagonal matrix W₁, or the precoding matrix Wis obtained by performing weighted combination on one or more columnvectors of a block diagonal matrix W₁, where W₁=diag {X₁, . . . ,X_(N)_(B) }, and N_(B)≥1, where at least one block matrix X is a Kroneckerproduct of a matrix A and a matrix B, X=A⊗B, and X ∈ {X₁,X₂, . . .,X_(N) _(B) }; the matrix A or the matrix B is a product of a matrix Dand a matrix V; the matrix D is a diagonal matrix, i=1, . . . ,n, and nis a quantity of rows of the matrix A or the matrix B, where

the matrix D is a diagonal matrix, D=α·diag {u₁,u₂, . . . ,u_(n),u_(n)*.u_(n−1)*, . . . ,u₁*}, α is a complex factor, a complex number u_(i)* is a conjugate complex number of a complex number u_(i), and n isdetermined by a quantity of antenna ports; and the matrix V is aconstant modulus matrix.

With reference to the fourteenth aspect, in a first possibleimplementation manner, in the second condition or the third condition,the precoding matrix W satisfies W=W₁W₂, where the matrix W₂ is used toselect one or more column vectors of the matrix W₁; or is used toperform weighted combination on one or more column vectors of the W₁ toobtain the precoding matrix W.

With reference to the fourteenth aspect or the first possibleimplementation manner of the fourteenth aspect, in a second possibleimplementation manner, phases of diagonal elements u₁,u₂, . . . ,u_(n)of the matrix D form an arithmetic progression.

With reference to the fourteenth aspect or either possibleimplementation manner of the fourteenth aspect, in a third possibleimplementation manner, the matrix V includes a column vector 1 and/or atleast one column vector v, the column vector 1 is a column vector whoseelements are all 1, and the column vector v is v=[v₁ v₂ L v_(n) v _(n) v_(n−1) L v ₁]^(T), where an element is v _(i)=−v_(i),v_(i)=±1, and i=1,. . . ,n.

With reference to the third possible implementation manner of theforegoing fourteenth aspect, in a fourth possible implementation manner,the matrix V includes only the column vector 1 and the at least onecolumn vector v, and when the matrix V includes multiple column vectorsv, the multiple column vectors v are different.

With reference to the third or fourth possible implementation manner ofthe foregoing fourteenth aspect, in a fifth possible implementationmanner, the column vector v of the matrix V is a column vector of amatrix [H^(T) H^(T)]^(T), where a matrix H is a Hadamard matrix.

With reference to any possible implementation manner of the foregoingfourteenth aspect, in a sixth possible implementation manner, theprecoding matrix indicator PMI includes a first index PMI1 and a secondindex PMI2, where

when the precoding matrix W satisfies the first condition, the firstindex PMI1 corresponds to the matrix D, and the second index PMI2corresponds to the matrix V;

when the precoding matrix W satisfies the second condition, the firstindex PMI1 corresponds to the matrix W₁, and the second index PMI2corresponds to the matrix W₂; or

when the precoding matrix W satisfies the third condition, the firstindex PMI1 corresponds to the matrix W₁, and the second index PMI2corresponds to the matrix W₂.

With reference to the sixth possible implementation manner of theforegoing fourteenth aspect, in a seventh possible implementationmanner, the first index PMI1 and the second index PMI2 have differenttime-domain granularities or frequency-domain granularities; or thefirst index PMI1 and the second index PMI2 are sent to the base stationby using different time periods.

With reference to the foregoing fourteenth aspect or any possibleimplementation manner of the fourteenth aspect, in an eighth possibleimplementation manner, the determining a corresponding precoding matrixW according to the PMI includes:

selecting the corresponding precoding matrix W from a codebook accordingto the PMI.

With reference to the eighth possible implementation manner of thefourteenth aspect, in a ninth possible implementation manner, thecodebook includes a precoding matrix W_(i) and a precoding matrix W_(j),and the two precoding matrices satisfy W_(i)=D(i,j)W_(j), whereD(i,j)=α_((i,j))diag {μ₁, μ₂, . . . ,μ_(n),μ_(n)*,μ_(n−1)*, . . . ,μ₁*},α_((i,j)) is a complex factor, a complex number μ_(m)* is a conjugatecomplex number of a complex number μ_(m), m=1, . . . ,n, and n isdetermined by a quantity of antenna ports.

With reference to the ninth possible implementation manner of thefourteenth aspect, in a tenth possible implementation manner, phases ofdiagonal elements μ₁,μ₂, . . . ,μ_(n) of the matrix D(i,j) form anarithmetic progression.

With reference to the eighth possible implementation manner of thefourteenth aspect, the codebook includes a precoding matrix W_(i) and aprecoding matrix W_(k), and the two precoding matrices satisfy D_(i)⁻¹W_(i)=D_(k) ⁻¹W_(k)=V, where D_(m)=α_(m)·diag {u_(m,1),u_(m,2), . . .,u_(m,n),u_(m,n)*,u_(m,n−1)*, . . . ,u_(m,1)*}, m=i,k, α_(m) is acomplex factor, a complex number u_(m,l)* is a conjugate complex numberof a complex number u_(m,l), m=i,k, l=1, . . . ,n, and n is determinedby a quantity of antenna ports.

With reference to the eleventh possible implementation manner of thefourteenth aspect, in a twelfth possible implementation manner, phasesof diagonal elements u_(m,1),u_(m,2), . . . ,u_(m,n) of the matrix D_(m)form an arithmetic progression.

A fifteenth aspect of the present invention provides user equipment,including:

a third processor, configured to determine a first precoding matrixindicator PMI, where the PMI corresponds to a precoding matrix W_(i) ina codebook; and

a second transmitter, configured to send the first PMI to a basestation, where

the codebook includes at least: the precoding matrix W_(i) and aprecoding matrix W_(j), and the precoding matrix W_(i) and the precodingmatrix W_(j) in the codebook satisfy W_(i)=D(i,j)W_(j), whereD(i,j)=α_((i,j))diag {μ₁,μ₂, . . . ,μ_(n),μ_(n)*,μ_(n−1)*, . . . ,μ₁*},α_((i,j)) is a complex factor, a complex number μ_(m)* is a conjugatecomplex number of a complex number μ_(m), m=1, . . . ,n, and n isdetermined by a quantity of antenna ports.

With reference to the fifteenth aspect, in a first possibleimplementation manner, phases of diagonal elements μ₁,μ₂, . . . ,μ_(n)of the matrix D(i,j) form an arithmetic progression.

A sixteenth aspect of the present invention provides a base station,including:

a third receiver, configured to receive a first precoding matrixindicator PMI sent by user equipment; and

a fourth processor, configured to determine a corresponding precodingmatrix W_(i) from a codebook according to the first PMI, where

the codebook includes at least: the precoding matrix W_(i) and aprecoding matrix W_(j), and the precoding matrix W_(i) and the precodingmatrix W_(j) in the codebook satisfy W_(i)=D(i,j)W_(j), whereD(i,j)=α_((i,j))diag {μ₁,μ₂, . . . ,μ_(n),μ_(n)*,μ_(n−1)*, . . . ,μ₁*},α_((i,j)) is a complex factor. a complex number μ_(m)* is a conjugatecomplex number of a complex number μ_(m), m=1, . . . ,n, and n isdetermined by a quantity of antenna ports.

With reference to the sixteenth aspect, in a first possibleimplementation manner, phases of diagonal elements μ₁,μ₂, . . .,μ_(n) ofthe matrix D(i,j) form an arithmetic progression.

A seventeenth aspect of the present invention provides user equipment,including:

a fifth processor, configured to determine a first precoding matrixindicator PMI, where the first PMI corresponds to a precoding matrixW_(i) in a codebook; and

a third transmitter, configured to send the first PMI to a base station,where

the codebook includes at least: the precoding matrix W_(i) and aprecoding matrix W_(j), and the precoding matrix W_(i) and a precodingmatrix in the codebook satisfy D_(i) ⁻¹W_(i)=D_(k) ⁻¹W_(k)=V, whereD_(m)=α_(m)·diag {u_(m,1),u_(m,2), . . . ,u_(m,n),u_(m,n)*,u_(m,n−1)*, .. . ,u_(m,1)*}, m=i,l, α_(m) is a complex factor, a complex numberu_(m,l)* is a conjugate complex number of a complex number u_(m,l),m=i,k, l=1, . . . ,n, n is determined by a quantity of antenna ports,and the matrix V is a constant modulus matrix.

With reference to the seventeenth aspect, in a first possibleimplementation manner, phases of diagonal elements u_(m,1),u_(m,2), . .. ,u_(m,n) of the matrix D_(m) form an arithmetic progression.

An eighteenth aspect of the present invention provides a base station,including:

a fourth receiver, configured to receive a first precoding matrixindicator PMI sent by user equipment; and

sixth processor, configured to determine a corresponding precodingmatrix W_(i) from a codebook according to the first PMI, where

the codebook includes at least: the precoding matrix W_(i) and aprecoding matrix W_(j), and the precoding matrix W_(i) and a precodingmatrix W_(k) in the codebook satisfy D_(i) ⁻¹W_(i)=D_(k) ⁻¹W_(k)=V,where D_(m)=α_(m)·diag {u_(m,1),u_(m,2), . . .,u_(m,n),u_(m,n)*,u_(m,n−1)*, . . . ,u_(m,1)*}, m=i,k, α_(m) is acomplex factor, a complex number u_(m,l)* is a conjugate complex numberof a complex number u_(m,l), m=i,k, l=1, . . . ,n, n is determined by aquantity of antenna ports, and the matrix V is a constant modulusmatrix.

With reference to the eighteenth aspect, in a first possibleimplementation manner, phases of diagonal elements u_(m,1),u_(m,2), . .. ,u_(m,n) of the matrix D_(m) form an arithmetic progression.

In the technical solutions provided in the embodiments of the presentinvention, a precoding matrix indicator PMI is determined, where the PMIcorresponds to a precoding matrix W, and the precoding matrix Wsatisfies a first condition, a second condition, or a third condition,where the first condition is that the precoding matrix W satisfies W=DV,where the matrix D is a diagonal matrix, D=α·diag {u₁,u₂, . . .,u_(n),u_(n)*,u_(n−1)*, . . . ,u₁*}, α is a complex factor, a complexnumber u_(i)* is a conjugate complex number of a complex number u_(i),and n is determined by a quantity of antenna ports; and the matrix V isa constant modulus matrix; the second condition is that the precodingmatrix W includes one or more column vectors of a block diagonal matrixW₁, or the precoding matrix W is obtained by performing weightedcombination on one or more column vectors of a block diagonal matrix W₁,where W₁=diag {X₁, . . . ,X_(N) _(B) }, and N_(B)≥1, where at least oneblock matrix X is a product X=DV of a matrix D and a matrix V, and X ∈{X₁,X₂, . . . ,X_(N) _(B) }; the matrix D is a diagonal matrix, D=α·diag{u₁,u₂, . . . ,u_(n),u_(n)*,u_(n−1)*, . . . ,u₁*}, α is a complexfactor, a complex number u_(i)* is a conjugate complex number of acomplex number u_(i), and n is determined by a quantity of antennaports; and the matrix V is a constant modulus matrix; and the thirdcondition is that the precoding matrix W includes one or more columnvectors of a block diagonal matrix W₁, or the precoding matrix W isobtained by performing weighted combination on one or more columnvectors of a block diagonal matrix W₁, where W₁=diag {X₁, . . . ,X_(N)_(B) }, and N_(B)≥1, where at least one block matrix X is a Kroneckerproduct of a matrix A and a matrix B, X=A⊗B, and X ∈ {X₁,X₂, . . .,X_(N) _(B) }; the matrix A or the matrix B is a product of a matrix Dand a matrix V; the matrix D is a diagonal matrix, D=α·diag {u₁,u₂, . .. ,u_(n),u_(n)*,u_(n−1)*, . . . ,u₁*}, α is a complex factor, a complexnumber u_(i)* is a conjugate complex number of a complex number u_(i),i=1, . . . ,n, and n is a quantity of rows of the matrix A or the matrixB; and the matrix V is a constant modulus matrix. A beam, especially abeam shape and a beam orientation, in a horizontal direction and aperpendicular direction can be effectively controlled.

BRIEF DESCRIPTION OF DRAWINGS

To describe the technical solutions in the embodiments of the presentinvention more clearly, the following briefly introduces theaccompanying drawings required for describing the embodiments.Apparently, the accompanying drawings in the following description showsome embodiments of the present invention, and a person of ordinaryskill in the art may still derive other drawings from these accompanyingdrawings without creative efforts.

FIG. 1 is a first schematic flowchart of a method for determining aprecoding matrix indicator according to an embodiment of the presentinvention;

FIG. 2 is a second schematic flowchart of a method for determining aprecoding matrix indicator according to an embodiment of the presentinvention;

FIG. 3 is a first schematic flowchart of a specific embodiment of thepresent invention;

FIG. 4 is a second schematic flowchart of a specific embodiment of thepresent invention;

FIG. 5 is a third schematic flowchart of a specific embodiment of thepresent invention;

FIG. 6 is a fourth schematic flowchart of a specific embodiment of thepresent invention;

FIG. 7 is a fifth schematic flowchart of a specific embodiment of thepresent invention;

FIG. 8 is a sixth schematic flowchart of a specific embodiment of thepresent invention;

FIG. 9 is a first schematic structural diagram of an apparatus fordetermining a precoding matrix indicator according to an embodiment ofthe present invention;

FIG. 10 is a second schematic structural diagram of an apparatus fordetermining a precoding matrix indicator according to an embodiment ofthe present invention;

FIG. 11 is a third schematic structural diagram of an apparatus fordetermining a precoding matrix indicator according to an embodiment ofthe present invention;

FIG. 12 is a fourth schematic structural diagram of an apparatus fordetermining a precoding matrix indicator according to an embodiment ofthe present invention;

FIG. 13 is a fifth schematic structural diagram of an apparatus fordetermining a precoding matrix indicator according to an embodiment ofthe present invention;

FIG. 14 is a sixth schematic structural diagram of an apparatus fordetermining a precoding matrix indicator according to an embodiment ofthe present invention;

FIG. 15 is a first schematic structural diagram of user equipmentaccording to an embodiment of the present invention;

FIG. 16 is a first schematic structural diagram of a base stationaccording to an embodiment of the present invention;

FIG. 17 is a second schematic structural diagram of user equipmentaccording to an embodiment of the present invention;

FIG. 18 is a second schematic structural diagram of a base stationaccording to an embodiment of the present invention;

FIG. 19 is a third schematic structural diagram of user equipmentaccording to an embodiment of the present invention; and

FIG. 20 is a third schematic structural diagram of a base stationaccording to an embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

To make the objectives, technical solutions, and advantages of theembodiments of the present invention clearer, the following clearlydescribes the technical solutions in the embodiments of the presentinvention with reference to the accompanying drawings in the embodimentsof the present invention. Apparently, the described embodiments are somebut not all of the embodiments of the present invention. All otherembodiments obtained by a person of ordinary skill in the art based onthe embodiments of the present invention without creative efforts shallfall within the protection scope of the present invention.

An embodiment of the present invention provides a method for determininga precoding matrix indicator. FIG. 1 is a first schematic flowchart ofthe method for determining a precoding matrix indicator according tothis embodiment of the present invention, and as shown in FIG. 1, themethod includes the following steps:

Step 101: User equipment determines a precoding matrix indicator PMI,where the PMI corresponds to a precoding matrix W, and the precodingmatrix W satisfies a first condition, a second condition, or a thirdcondition.

Step 102: The user equipment sends the PMI to a base station.

The first condition is that the precoding matrix W satisfies W=DV; thesecond condition is that the precoding matrix W includes one or morecolumn vectors of a block diagonal matrix W₁, or the precoding matrix Wis obtained by performing weighted combination on one or more columnvectors of a block diagonal matrix W₁, where W₁=diag {X₁, . . . ,X_(N)_(B) }, and N_(B)≥1, where at least one block matrix X is a product X=DVof a matrix D and a matrix V, and X ∈ {X₁,X₂, . . . ,X_(N) _(B) }; andthe third condition is that the precoding matrix W includes one or morecolumn vectors of a block diagonal matrix W₁, or the precoding matrix Wis obtained by performing weighted combination on one or more columnvectors of a block diagonal matrix W₁, where W₁=diag {X₁, . . . ,X_(N)_(B) }, and N_(B)≥1, where at least one block matrix X is a Kroneckerproduct of a matrix A and a matrix B, X=A⊗B, and X ∈ {X₁, X₂, . . .,X_(N) _(B) }; the matrix A or the matrix B is a product of a matrix Dand a matrix V; the matrix D is a diagonal matrix, i=1, . . . ,n, and nis a quantity of rows of the matrix A or the matrix B, where

the matrix D is a diagonal matrix, D=α·diag {u₁,u₂, . . . ,u_(n),u_(n)*, u_(n−1)*, . . . ,u₁*}, α is a complex factor, a complex numberu_(i)* is a conjugate complex number of a complex number u_(i), and n isdetermined by a quantity of antenna ports; and the matrix V is aconstant modulus matrix.

In this embodiment, for detailed descriptions about three cases in whichthe precoding matrix W separately satisfies the first condition, thesecond condition, and the third condition, reference may be made to thefollowing specific embodiments.

In addition, the method, provided in this embodiment of the presentinvention, for determining a precoding matrix indicator may furtherinclude: receiving a reference signal sent by the base station, andselecting, from a codebook according to the reference signal, theprecoding matrix W corresponding to the PMI. Then, the determining aprecoding matrix indicator PMI in the foregoing step 101 isspecifically: determining the PMI according to the reference signal orthe precoding matrix W.

Alternatively, the method, provided in this embodiment of the presentinvention, for determining a precoding matrix indicator may furtherinclude: receiving a reference signal sent by the base station. Then,the determining a precoding matrix indicator PMI in the foregoing step101 is specifically: determining the precoding matrix indicator PMIaccording to the reference signal. In addition, after the determiningthe PMI according to the reference signal, the method further includes:determining the precoding matrix W according to the reference signal orthe precoding matrix indicator PMI.

Corresponding to the embodiment, shown in FIG. 1, of the method on auser equipment side, the present invention further provides a method fordetermining a precoding matrix indicator on a base station side. FIG. 2is a second schematic flowchart of the method for determining aprecoding matrix indicator according to an embodiment of the presentinvention, and as shown in FIG. 2, the method includes the followingsteps:

Step 201: Receive a precoding matrix indicator PMI sent by userequipment.

Step 202: Determine a corresponding precoding matrix W according to thePMI, where the precoding matrix W satisfies a first condition, a secondcondition, or a third condition.

The first condition is that the precoding matrix W satisfies W=DV;

the second condition is that the precoding matrix W includes one or morecolumn vectors of a block diagonal matrix W₁, or the precoding matrix Wis obtained by performing weighted combination on one or more columnvectors of a block diagonal matrix W₁, where W₁=diag {X₁, . . . ,X_(N)_(B) } and N_(B)≥1, where at least one block matrix X is a product X=DVof a matrix D and a matrix V, and X ∈ {X₁,X₂, . . . ,X_(N) _(B) }; and

the third condition is that the precoding matrix W includes one or morecolumn vectors of a block diagonal matrix W₁, or the precoding matrix Wis obtained by performing weighted combination on one or more columnvectors of a block diagonal matrix W₁, where W₁=diag {X₁, . . . ,X_(N)_(B) }, and N_(B)≥1, where at least one block matrix X is a Kroneckerproduct of a matrix A and a matrix B, X=A⊗B, and X ∈ {X₁X₂, . . . ,X_(N)_(B) }; the matrix A or the matrix B is a product of a matrix D and amatrix V; the matrix D is a diagonal matrix, i=1, . . . ,n, and n is aquantity of rows of the matrix A or the matrix B, where

the matrix D is a diagonal matrix, D=α·diag {u₁,u₂, . . . ,u_(n),u_(n)*, u_(n−1)*, . . . ,u₁*}, α is a complex factor, a complex numberu_(i)* is a conjugate complex number of a complex number u_(i), and n isdetermined by a quantity of antenna ports; and the matrix V is aconstant modulus matrix.

In the foregoing embodiment, for detailed descriptions about three casesin which the precoding matrix W separately satisfies the firstcondition, the second condition, and the third condition, reference maybe made to the following specific embodiments. In addition, thedetermining a corresponding precoding matrix W according to the PMI inthe foregoing step 202 may be specifically: selecting the correspondingprecoding matrix W from a codebook according to the PMI.

FIG. 3 is a first schematic flowchart of a specific embodiment. Thisembodiment provides a method for determining a precoding matrixindicator that is executed on a user equipment side when a precodingmatrix satisfies a first condition. As shown in FIG. 3, the methodincludes:

Step 301: User equipment receives a reference signal sent by a basestation.

Specifically, the reference signal sent by the base station in this stepmay include: a channel state information reference signal (CSI RS), ademodulation reference signal (DM RS), or a cell-specific referencesignal (CRS). The user equipment UE may acquire the reference signal byreceiving a reference signal resource configuration notified by an eNB,or obtain a resource configuration of the reference signal according toa cell identity (cellID) and obtain the reference signal in acorresponding resource or subframe, where the eNB notification may behigher-layer signaling such as radio resource control (RRC) signaling,or dynamic signaling such as downlink control information (DCI). Thehigher-layer signaling is sent to the user equipment by using a physicaldownlink shared channel (PDSCH). The DCI may be sent to the userequipment by using a physical downlink control channel (PDCCH) or anenhanced PDCCH (ePDCCH).

Step 302: The user equipment selects, based on the reference signal, aprecoding matrix from a codebook.

In this embodiment of the present invention, the codebook is a set of anavailable precoding matrix. The codebook and the PMI may be stored in adevice in a table lookup manner; or a device may obtain thecorresponding PMI by means of calculation by using a preset formula oralgorithm according to the codebook, or obtain the correspondingcodebook by means of calculation according to the PMI.

In an optional implementation manner of this embodiment, at least oneprecoding matrix W included in the codebook is a product of a matrix Dand a matrix V ; and has the structure shown in formula (1):W=DV  (1)

where the matrix D is a diagonal matrix, and satisfies:D=α·diag{u ₁ ,u ₂ , . . . ,u _(n) ,u _(n) *,u _(n−1) *, . . . ,u₁*}  (2)

where α is a complex factor, and a real part or an imaginary part of thecomplex factor may be 0; a complex number u_(i)* is a conjugate complexnumber of a complex number u_(i), and i=1, . . . ,n; and the matrix V isa constant modulus matrix, for example, elements of the matrix V maybe±1 or ±j.

It should be noted that, the so-called constant modulus matrix refers toa matrix whose elements have a same module or amplitude. It should beunderstood that, a constant modulus matrix generally is a non-diagonalmatrix, or certainly, may be a diagonal matrix, for example, theconstant modulus matrix is a matrix whose elements are 0.

In another optional implementation manner of this embodiment, the matrixV includes a column vector 1 and/or at least one column vector v, wherethe column vector 1 is a column vector whose elements are all 1, and thecolumn vector v is:v=[v ₁ v ₂ L v _(n) v _(n) v _(n−1) L v ₁]^(T),  (3)

where ( )^(T) represents transposition of a matrix or vector, an elementis v _(i)=−v_(i), i=1, . . . ,n, and v_(i)=±1, that is, a value of v_(i)is +1 or −1. In an exemplary implementation manner, the matrix V isformed only by the column vector 1 and/or the at least one column vectorv. That is, in the matrix V, except the included column vector 1, theother column vectors are column vectors v. Further, preferably, when thematrix V includes multiple vectors v, the multiple vectors v_(s) aredifferent; in this case, better orthogonality can be provided, therebyavoiding occurrence of strong interference.

In another optional implementation manner of this embodiment, thecodebook includes at least: a precoding matrix W_(i) and a precodingmatrix W_(j), where the W_(i) and the W_(j) satisfy the formula (4):W _(i) =D(i,j)W _(i)  (4)

where the matrix D(i,j) is a diagonal matrix; optionally, phases ofdiagonal elements μ₁,μ₂, . . . ,μ_(n) of the matrix D(i,j) form anarithmetic progression, and the matrix has the structure shown in theformula (5):D(i,j)=α_((i,j))diag{μ₁,μ₂, . . . ,μ_(n),μ_(n)*,μ_(n−1)*, . . .,μ₁*}  (5)

where α_((i,j)) is a complex factor, and a real part or an imaginarypart of the complex factor may be 0; and a complex number μ_(m)* is aconjugate complex number of a complex number μ_(m), m=1, . . . ,n, and nis determined by a quantity of antenna ports.

For the foregoing two precoding matrices in the codebook, the userequipment may select different precoding matrices from the codebook atdifferent time points according to a preset rule or randomly, that is,the user equipment may determine a first precoding matrix indicator PMIat a time point, where the PMI corresponds to the precoding matrix W_(i)in the codebook, and send the first PMI to the base station; anddetermine a second precoding matrix indicator PMI at another time point,where the PMI corresponds to the precoding matrix W_(j) in the codebook,and send the second PMI to the base station.

Corresponding to the case in which the foregoing user equipment sendsthe first PMI or the second PMI at different time points, on a basestation side, the base station may also receive, at a time point, thefirst precoding matrix indicator PMI sent by the user equipment, andselect the corresponding precoding matrix W_(i) from the codebookaccording to the first PMI; and receive, at another time point, thesecond precoding matrix indicator PMI sent by the user equipment, andselect the corresponding precoding matrix W_(j) from the codebookaccording to the second PMI.

Optionally, the codebook includes at least: a precoding matrix W_(i) anda precoding matrix W_(k), where the W_(i) and W_(k) satisfy the formula(6):D _(i) ⁻¹ W _(i) =D _(k) ⁻¹ W _(k) =V  (6)

where the matrix V includes a column vector 1 and/or at least one columnvector v, the column vector 1 is a column vector whose elements are all1, and the column vector v has the structure shown in the formula (3);and the matrix D_(i) and the matrix D_(k) both are diagonal matrices,and have the structure shown in the formula (7):D _(m)=α_(m)·diag{u _(m,1) ,u _(m,2) , . . . ,u _(m,n) ,u _(m,n) *,u_(m,n−1) *, . . . ,u _(m,1) *},m=i,k  (7)

where α_(m) is a complex factor, and a real part or an imaginary part ofthe complex factor may be 0; a complex number u_(m,l)* is a conjugatecomplex number of a complex number u_(m,l), m=i,k, l=1, . . . ,n, and nis determined by a quantity of antenna ports; and optionally, phases ofdiagonal elements u_(m,1),u_(m,2), . . . ,u_(m,n) of the matrix D_(m)form an arithmetic progression.

For the foregoing two precoding matrices in the codebook, the userequipment may select different precoding matrices from the codebook atdifferent time points according to a preset rule or randomly, that is,the user equipment may determine a first precoding matrix indicator PMIat a time point, where the PMI corresponds to the precoding matrix W_(i)in the codebook, and send the first PMI to the base station; anddetermine a second precoding matrix indicator PMI at another time point,where the PMI corresponds to the precoding matrix W_(k) in the codebook,and send the second PMI to the base station.

Corresponding to the case in which the foregoing user equipment sendsthe first PMI or the second PMI at different time points, on a basestation side, the base station may also receive, at a time point, thefirst precoding matrix indicator PMI sent by the user equipment, andselect the corresponding precoding matrix W_(i) from the codebookaccording to the first PMI; and receive, at another time point, thesecond precoding matrix indicator PMI sent by the user equipment, andselect the corresponding precoding matrix W_(k) from the codebookaccording to the second PMI.

It should be pointed out that diagonal elements of the foregoingdiagonal matrix may have same amplitude. In this case, the structure ofthe foregoing precoding matrix allows that transmit antennascorresponding to rows of the precoding matrix have symmetric transmitpowers based on actual considerations, and in this case, the foregoingcodebook can still control a beam orientation by using a symmetricproperty of the powers of the transmit antennas, and meanwhile ensureorthogonality between transmission layers.

Step 303: The user equipment sends a precoding matrix indicator PMI tothe base station, where the PMI corresponds to the selected precodingmatrix.

In the foregoing embodiment of the present invention, user equipmentselects, based on a reference signal, a precoding matrix from acodebook, and sends a precoding matrix indicator PMI. A precoding matrixW included in the codebook is a product of a matrix D and a matrix V.The D is a diagonal matrix and satisfies D=α·diag {u₁,u₂, . . .,u_(n),u_(n)*,u_(n−1)*, . . . ,u₁*}, where u₁,u₂, . . .,u_(n),u_(n)*u_(n−1)*, . . . ,u₁* forms a conjugate and symmetricsequence, which avoids constant modulus restrictions or a limit thatantennas perform transmission by using equal powers, and can effectivelycontrol a beam shape and a beam orientation.

Further, the matrix V includes a column vector 1 and/or at least onecolumn vector v=[v₁ v₂ L v_(n) v _(n) v _(n−1) L v ₁]^(T), so thatcolumn vectors of the precoding matrix are orthogonal to each other,which can effectively reduce inter-layer interference, thereby greatlyimproving performance of MIMO, especially MU-MIMO. Therefore, theforegoing method for determining a precoding matrix can fully use adegree of freedom of controlling a beam shape and a beam orientation ofan antenna system, and meanwhile reduce inter-layer interference of MIMOtransmission as much as possible, thereby improving precision of CSIfeedback, and a system throughput.

Using n=5 as an example, diagonal elements shown in the formula (2) maybe:

$\begin{matrix}{\left\lbrack {u_{1},u_{2},u_{3},u_{4},u_{5}} \right\rbrack = \left\lbrack {e^{j\frac{\pi}{2}},{\left( \frac{7}{6} \right)^{\frac{1}{2}}e^{j\frac{\pi}{3}}},{\left( \frac{8}{6} \right)^{\frac{1}{2}}e^{j\frac{\pi}{4}}},{\left( \frac{9}{6} \right)^{\frac{1}{2}}e^{j\frac{\pi}{6}}},\left( \frac{10}{6} \right)^{\frac{1}{2}}} \right\rbrack} & (8)\end{matrix}$

correspondingly, the following formula is satisfied:

$\begin{matrix}{\left\lbrack {u_{5}^{*},u_{4}^{*},u_{3}^{*},u_{2}^{*},u_{1}^{*}} \right\rbrack = \left\lbrack {\left( \frac{10}{6} \right)^{\frac{1}{2}},{\left( \frac{9}{6} \right)^{\frac{1}{2}}e^{{- j}\frac{\pi}{6}}},{\left( \frac{8}{6} \right)^{\frac{1}{2}}e^{{- j}\frac{\pi}{4}}},{\left( \frac{7}{6} \right)^{\frac{1}{2}}e^{{- j}\frac{\pi}{3}}},e^{{- j}\frac{\pi}{2}}} \right\rbrack} & (9)\end{matrix}$

Alternatively, diagonal elements shown in the formula (2) may be:

$\begin{matrix}{\left\lbrack {u_{1},u_{2},u_{3},u_{4},u_{5}} \right\rbrack = \left\lbrack {e^{j\frac{\pi}{2}},e^{j\frac{\pi}{3}},e^{j\frac{\pi}{4}},e^{j\frac{\pi}{6}},1} \right\rbrack} & (10)\end{matrix}$

correspondingly, the following formula is satisfied:

$\begin{matrix}{\left\lbrack {u_{5}^{*},u_{4}^{*},u_{3}^{*},u_{2}^{*},u_{1}^{*}} \right\rbrack = \left\lbrack {1,e^{{- j}\frac{\pi}{6}},e^{{- j}\frac{\pi}{4}},e^{{- j}\frac{\pi}{3}},e^{{- j}\frac{\pi}{2}}} \right\rbrack} & (11)\end{matrix}$

Correspondingly, the column vector v may be:v=[1 1 1 1 1 −1 −1 −1 −1 −1]^(T)  (12)

Optionally, as another embodiment, in the matrix D, phases of thediagonal elements u₁,u₂,. . . . ,u_(n) form an arithmetic progression,and phases of the diagonal elements u_(n)*,u_(n−1)*, . . . ,u₁* form anarithmetic progression.

Using n=5 as an example, diagonal elements shown in the formula (5) maybe:

$\begin{matrix}{\left\lbrack {\mu_{1},\mu_{2},\mu_{3},\mu_{4},\mu_{5}} \right\rbrack = \left\lbrack {e^{j\frac{\pi}{2}},{\left( \frac{7}{6} \right)^{\frac{1}{2}}e^{j\frac{\pi}{3}}},{\left( \frac{8}{6} \right)^{\frac{1}{2}}e^{j\frac{\pi}{4}}},{\left( \frac{9}{6} \right)^{\frac{1}{2}}e^{j\frac{\pi}{6}}},\left( \frac{10}{6} \right)^{\frac{1}{2}}} \right\rbrack} & \left( {8a} \right)\end{matrix}$

correspondingly, the following formula is satisfied:

$\begin{matrix}{\left\lbrack {\mu_{5}^{*},\mu_{4}^{*},\mu_{3}^{*},\mu_{2}^{*},\mu_{1}^{*}} \right\rbrack = \left\lbrack {\left( \frac{10}{6} \right)^{\frac{1}{2}},{\left( \frac{9}{6} \right)^{\frac{1}{2}}e^{{- j}\frac{\pi}{6}}},{\left( \frac{8}{6} \right)^{\frac{1}{2}}e^{{- j}\frac{\pi}{4}}},{\left( \frac{7}{6} \right)^{\frac{1}{2}}e^{{- j}\frac{\pi}{3}}},e^{{- j}\frac{\pi}{2}}} \right\rbrack} & \left( {9a} \right)\end{matrix}$

Alternatively, diagonal elements shown in the formula (5) may be:

$\begin{matrix}{\left\lbrack {\mu_{1},\mu_{2},\mu_{3},\mu_{4},\mu_{5}} \right\rbrack = \left\lbrack {e^{j\frac{\pi}{2}},e^{j\frac{\pi}{3}},e^{j\frac{\pi}{4}},e^{j\frac{\pi}{6}},1} \right\rbrack} & \left( {10a} \right)\end{matrix}$

correspondingly, the following formula is satisfied:

$\begin{matrix}{\left\lbrack {\mu_{5}^{*},\mu_{4}^{*},\mu_{3}^{*},\mu_{2}^{*},\mu_{1}^{*}} \right\rbrack = \left\lbrack {1,e^{{- j}\frac{\pi}{6}},e^{{- j}\frac{\pi}{4}},e^{{- j}\frac{\pi}{3}},e^{{- j}\frac{\pi}{2}}} \right\rbrack} & (11)\end{matrix}$

Using n=4 as an example, diagonal elements shown in the formula (2) maybe:

$\begin{matrix}{\left\lbrack {u_{1},u_{2},u_{3},u_{4}} \right\rbrack = \left\lbrack {e^{j\frac{7\pi}{12}},{\left( \frac{5}{4} \right)^{\frac{1}{2}}e^{j\frac{5\pi}{12}}},{\left( \frac{6}{4} \right)^{\frac{1}{2}}e^{j\frac{3\pi}{12}}},{\left( \frac{7}{4} \right)^{\frac{1}{2}}e^{j\frac{\pi}{12}}}} \right\rbrack} & (13)\end{matrix}$

correspondingly, the following formula is satisfied:

$\begin{matrix}{\left\lbrack {u_{4}^{*},u_{3}^{*},u_{2}^{*},u_{1}^{*}} \right\rbrack = \left\lbrack {{\left( \frac{7}{4} \right)^{\frac{1}{2}}e^{{- j}\frac{\pi}{12}}},{\left( \frac{6}{4} \right)^{\frac{1}{2}}e^{{- j}\frac{3\pi}{12}}},{\left( \frac{5}{4} \right)^{\frac{1}{2}}e^{{- j}\frac{5\pi}{12}}},e^{{- j}\frac{7\pi}{12}}} \right\rbrack} & (14)\end{matrix}$

Alternatively, diagonal elements shown in the formula (2) are:

$\begin{matrix}{\left\lbrack {u_{1},u_{2},u_{3},u_{4}} \right\rbrack = \left\lbrack {e^{j\frac{7\pi}{12}},e^{j\frac{5\pi}{12}},e^{j\frac{3\pi}{12}},e^{j\frac{\pi}{12}}} \right\rbrack} & (15)\end{matrix}$

correspondingly, the following formula is satisfied:

$\begin{matrix}{\left\lbrack {u_{4}^{*},u_{3}^{*},u_{2}^{*},u_{1}^{*}} \right\rbrack = \left\lbrack {e^{{- j}\frac{\pi}{12}},e^{{- j}\frac{3\pi}{12}},e^{{- j}\frac{5\pi}{12}},e^{{- j}\frac{7\pi}{12}}} \right\rbrack} & (16)\end{matrix}$

In the foregoing two formulas, a phase of the diagonal elements u₁,u₂, .. . ,u_(n) and a phase progression of the diagonal elements u_(n)*,u_(n−1)*, . . . ,u₁* respectively form arithmetic progressions whosecommon differences respectively are −π/6 and +π/6.

Using n=4 as an example, diagonal elements shown in the formula (5) maybe:

$\begin{matrix}{\left\lbrack {\mu_{1},\mu_{2},\mu_{3},\mu_{4}} \right\rbrack = \left\lbrack {e^{j\frac{7\pi}{32}},{\left( \frac{5}{4} \right)^{\frac{1}{2}}e^{j\frac{5\pi}{32}}},{\left( \frac{6}{4} \right)^{\frac{1}{2}}e^{j\frac{3\pi}{32}}},{\left( \frac{7}{4} \right)^{\frac{1}{2}}e^{j\frac{\pi}{32}}}} \right\rbrack} & \left( {13a} \right)\end{matrix}$

correspondingly, the following formula is satisfied:

$\begin{matrix}{\left\lbrack {\mu_{4}^{*},\mu_{3}^{*},\mu_{2}^{*},\mu_{1}^{*}} \right\rbrack = \left\lbrack {{\left( \frac{7}{4} \right)^{\frac{1}{2}}e^{{- j}\frac{\pi}{32}}},{\left( \frac{6}{4} \right)^{\frac{1}{2}}e^{{- j}\frac{3\pi}{32}}},{\left( \frac{5}{4} \right)^{\frac{1}{2}}e^{{- j}\frac{5\pi}{32}}},e^{{- j}\frac{7\pi}{32}}} \right\rbrack} & \left( {14a} \right)\end{matrix}$

Alternatively, diagonal elements shown in the formula (5) are:

$\begin{matrix}{\left\lbrack {\mu_{1},\mu_{2},\mu_{3},\mu_{4}} \right\rbrack = \left\lbrack {e^{j\frac{7\pi}{32}},e^{j\frac{5\pi}{32}},e^{j\frac{3\pi}{32}},e^{j\frac{\pi}{32}}} \right\rbrack} & \left( {15a} \right)\end{matrix}$

correspondingly, the following formula is satisfied:

$\begin{matrix}{\left\lbrack {\mu_{4}^{*},\mu_{3}^{*},\mu_{2}^{*},\mu_{1}^{*}} \right\rbrack = \left\lbrack {e^{{- j}\frac{\pi}{32}},e^{{- j}\frac{3\pi}{32}},e^{{- j}\frac{5\pi}{32}},e^{{- j}\frac{7\pi}{32}}} \right\rbrack} & \left( {16a} \right)\end{matrix}$

In the foregoing two formulas, a phase of the diagonal elements u₁,u₂, .. . ,u_(n) and a phase progression of the diagonal elementsu_(n)*,u_(n−1)*, . . . ,u₁* respectively form arithmetic progressionswhose common differences respectively are −π/16 and π/16.

Using n=4 as an example, diagonal elements of the diagonal matricesshown in the formula (7) may be respectively:

$\begin{matrix}{\mspace{79mu}{\left\lbrack {\mu_{i,1},\mu_{i,2},\mu_{i,3},\mu_{i,4}} \right\rbrack = \left\lbrack {e^{j\frac{7\pi}{16}},{\left( \frac{5}{4} \right)^{\frac{1}{2}}e^{j\frac{5\pi}{16}}},{\left( \frac{6}{4} \right)^{\frac{1}{2}}e^{j\frac{3\pi}{16}}},{\left( \frac{7}{4} \right)^{\frac{1}{2}}e^{j\frac{\pi}{16}}}} \right\rbrack}} & (17) \\{\left\lbrack {\mu_{k,1},\mu_{k,2},\mu_{k,3},\mu_{k,4}} \right\rbrack = \left\lbrack {e^{j\frac{7\pi}{8}},{\left( \frac{5}{4} \right)^{\frac{1}{2}}e^{j\frac{5\pi}{8}}},{\left( \frac{6}{4} \right)^{\frac{1}{2}}e^{j\frac{3\pi}{8}}},{\left( \frac{7}{4} \right)^{\frac{1}{2}}e^{j\frac{\pi}{8}}}} \right\rbrack} & (18)\end{matrix}$

Alternatively, diagonal elements of the diagonal matrices shown in theformula (7) may be respectively:

$\begin{matrix}{\left\lbrack {\mu_{i,1},\mu_{i,2},\mu_{i,3},\mu_{i,4}} \right\rbrack = \left\lbrack {e^{j\frac{7\pi}{16}},e^{j\frac{5\pi}{16}},e^{j\frac{3\pi}{16}},e^{j\frac{\pi}{16}}} \right\rbrack} & (19) \\{\left\lbrack {\mu_{k,1},\mu_{k,2},\mu_{k,3},\mu_{k,4}} \right\rbrack = \left\lbrack {e^{j\frac{7\pi}{8}},e^{j\frac{5\pi}{8}},e^{j\frac{3\pi}{8}},e^{j\frac{\pi}{8}}} \right\rbrack} & (20)\end{matrix}$

In this embodiment, in the matrix D, the phases of the diagonal elementsu₁,u₂, . . . ,u_(n) form an arithmetic progression, and the phases ofthe diagonal elements u_(n)*,u_(n−1)*, . . . ,u₁* form an arithmeticprogression, which may match with an array structure of an antenna port,for example, a common uniform linear array or cross polarization array,where in the former array, array elements or antennas are arranged at asame spacing, and in the latter array, co-polarized antennas or arrayelements are arranged at a same spacing. Therefore, the phases in thearithmetic progression can improve precoding performance by using aproperty of the foregoing array structure.

Optionally, as another embodiment, the column vector v of the matrix Vmay be a column vector of a matrix [H^(T) H^(T)]^(T), where a matrix His a Hadamard matrix.

Using n =4 as an example, the column vector v is a column vector of thematrix [H^(T) H^(T)]^(T), where

$\begin{matrix}{H = \begin{bmatrix}1 & 1 & 1 & 1 \\1 & {- 1} & 1 & {- 1} \\1 & 1 & {- 1} & {- 1} \\1 & {- 1} & {- 1} & 1\end{bmatrix}} & (21)\end{matrix}$

In this case, the column vector v may be:v=[1 −1 1 −1 1 −1 1 −1]^(T)  (22)

or,v=[1 1 −1 −1 1 1 −1 −1]^(T)  (23)

or,v=[1 −1 −1 1 1 −1 −1 1]^(T)  (24)

In this embodiment, the column vector v is a column vector of the matrix[H^(T) H^(T)]^(T), and satisfies the property of the formula (3), andcolumn vectors of the [H^(T) H^(T)]^(T) are orthogonal to each other, sothat the obtained column vectors are orthogonal to each other, therebyreducing inter-layer interference that is generated when the precodingmatrix is used for MIMO transmission.

In the foregoing embodiment of the present invention, the selecting, bythe user equipment, a precoding matrix from a codebook according to thereference signal may be specifically: obtaining, by the user equipmentbased on the reference signal, channel estimation; and selecting, basedon a predefined criterion according to the channel estimation, theprecoding matrix from the codebook, where the foregoing predefinedcriterion may be a channel capacity maximization criterion, a throughputmaximization criterion, or a cosine distance minimization criterion.

In addition, in this embodiment of the present invention, the selecting,based on the reference signal, a precoding matrix from a codebook mayinclude:

selecting the precoding matrix from a codebook subset according to thereference signal, where the foregoing codebook subset is a predefinedcodebook subset, or a codebook subset reported to the base station, or acodebook subset reported to the base station, and returned and confirmedby the base station; the foregoing predefined codebook subset may bepredefined in a protocol and is known by the user equipment and the basestation in the system; and the codebook subset reported to the basestation may be a codebook subset that is determined by the userequipment and is recently (recently) reported to the base station. Inthis embodiment, codebook subsets are set, for different applicationscenarios, in the codebook; and therefore, selecting a precoding matrixbased on a codebook subset can effectively reduce feedback overheads andthe implementation complexity.

Further, the codebook subset in the foregoing embodiment of the presentinvention may include a set of the precoding matrix W=DV; where thematrix D belongs to a subset of a universal set of the matrix D, or thematrix V belongs to a subset of a universal set of the matrix V.

It should be pointed out that diagonal elements of the foregoingdiagonal matrix may have same amplitude. In this case, the structure ofthe foregoing precoding matrix allows that transmit antennascorresponding to rows of the precoding matrix have symmetric transmitpowers based on actual considerations, and in this case, the foregoingcodebook can still control a beam orientation by using a symmetricproperty of the powers of the transmit antennas, and meanwhile ensureorthogonality between transmission layers.

It should be understood that the precoding matrix in the codebook or thecodebook subset may be pre-stored in the user equipment and the basestation, or may be calculated by the user equipment and the base stationaccording to the structure of the foregoing precoding matrix, or may beacquired from a network device, which is not limited in the presentinvention.

In step 303 shown in the foregoing FIG. 3, the precoding matrixindicator sent to the base station may include one or more indexes.Specifically, the codebook or the codebook subset usually is a set ofone or more precoding matrices, where one precoding matrix indicatorcorresponds to one precoding matrix. Different precoding matrixindicators correspond to different precoding matrices in the codebook orthe codebook subset, and in this embodiment, the sent precoding matrixindicator corresponds to the selected precoding matrix.

Specifically, the foregoing precoding matrix indicator PMI may includeonly one index, that is, one index directly indicates one precodingmatrix, or the foregoing precoding matrix indicator may include twoindexes, namely a first index PMI1 and a second index PMI2, where thefirst index PMI1 and the second index PMI2 jointly indicate theprecoding matrix. In addition, the first index PMI1 corresponds to thematrix D. and the second index PMI2 corresponds to the matrix V. In animplementation manner of this implementation manner, for precodingmatrices W indicated by two PMIs that have different first indexes PMI1and a same second index PMI2, corresponding matrices D are different,and corresponding matrices V are the same. Optionally, for precodingmatrices W indicated by two PMIs that have a same first index PMI1 anddifferent second indexes PMI2, corresponding matrices D are the same,and corresponding matrices V are different.

Optionally, the foregoing first index PMI1 and second index PMI2 mayhave different time-domain granularities or frequency-domaingranularities, that is, the PMI1 and the PMI2 separately representchannel characteristics of different periods or bandwidths, or areobtained based on different subframe periods or subbands.

Optionally, as another embodiment, the user equipment sends the firstindex PMI1 and the second index PMI2 to the base station by usingdifferent time periods, for example, the PMI1 may have a longer subframeperiod than the PMI2.

In addition, in step 303 in the foregoing embodiment of the presentinvention, the precoding matrix indicator PMI may be sent to the basestation by using a physical uplink control channel (PUCCH) or a physicaluplink shared channel (PUSCH).

The precoding matrix W in this embodiment may be a precoding matrixobtained by means of row or column transposition, for example, differentantenna numbers correspondingly cause row transposition of the precodingmatrix. In addition, the structure of the foregoing precoding matrix Wnot only may be used for antenna configuration in a horizontal directionin an AAS base station, but also may be used for antenna configurationin a perpendicular direction.

FIG. 4 is a second schematic flowchart of a specific embodiment. Asshown in FIG. 4, the embodiment includes the following steps:

Step 401: A base station sends a reference signal to user equipment.

Specifically, the reference signal sent by the base station in this stepmay include a CSI RS, a DM RS, or a CRS. The user equipment UE mayacquire the reference signal by receiving an eNB notification, or mayobtain, based on a cell identity ID, a resource configuration of thereference signal and obtain the reference signal in a correspondingresource or subframe, where the eNB notification may be higher-layersignaling such as RRC signaling, or dynamic signaling such as DCI.

Step 402: The base station receives a precoding matrix indicator PMIsent by the user equipment.

Specifically, the precoding matrix indicator PMI corresponds to aprecoding matrix that is selected from a codebook by the user equipmentbased on the reference signal.

Step 403: The base station determines a precoding matrix from a codebookaccording to the PMI, where the codebook includes one precoding matrix Wthat is a product of a matrix D and a matrix V and has the structureshown in the formula (25):W=DV  (25)

where the matrix D is a diagonal matrix, and satisfies:D=α·diag{u ₁ ,u ₂ , . . . ,u _(n) ,u _(n−1) *, . . . ,u ₁*}  (26)

where α is a complex factor, a complex number u₁* is a conjugate complexnumber of a complex number u_(i), and i=1, . . . ,n; and the matrix V isa constant modulus matrix, for example, elements of the matrix V maybe±1 or ±j.

In another optional implementation manner of this embodiment, the matrixV includes a column vector 1 and/or at least one column vector v, wherethe column vector 1 is a column vector whose elements are all 1, and thecolumn vector v is:v=[v ₁ v ₂ L v _(n) v _(n) v _(n−1) L v ₁]^(T)  (27)

where ( )^(T) represents transposition of a matrix or vector, an elementis v _(i)=−v_(i,), i=1, . . . , n, and v_(i)=±1, that is, a value ofv_(i) is +1 or −1. In an exemplary implementation manner, the matrix Vis formed only by the column vector 1 and/or the at least one columnvector v, that is, in the matrix V, except the included column vector 1,the other column vectors are all column vectors v.

In another optional implementation manner of this embodiment, thecodebook includes multiple precoding matrices, and the multipleprecoding matrices include a precoding matrix W_(i) and a precodingmatrix W_(j), where the W_(i) and the W_(j) satisfy the formula (4), andthe matrix D(i,j) is a diagonal matrix and has the structure shown inthe formula (5).

Optionally, the multiple precoding matrices include a precoding matrixW_(i) and a precoding matrix W_(k), where the W_(i) and the W_(k)satisfy the formula (6), the matrix v includes a column vector 1 and/orat least one column vector v, the column vector 1 is a column vectorwhose elements are all 1, and the column vector v has the structureshown in the formula (27). The matrix D_(i) and the matrix D_(k) bothare diagonal matrices, and have the structure shown in the formula (7).

It should be pointed out that diagonal elements of the foregoingdiagonal matrix may have same amplitude. In this case, the structure ofthe foregoing precoding matrix allows that transmit antennascorresponding to rows of the precoding matrix have symmetric transmitpowers based on actual considerations, and in this case, the foregoingcodebook can still control a beam orientation by using a symmetricproperty of the powers of the transmit antennas, and meanwhile ensureorthogonality between transmission layers.

In the foregoing embodiment of the present invention, a base stationreceives a precoding matrix indicator PMI sent by user equipment, anddetermines a precoding matrix from a codebook according to the PMI. Aprecoding matrix W included in the codebook is a product of a matrix Dand a matrix V. The D is a diagonal matrix and satisfies D=α·diag{u₁,u₂, . . . ,u_(n),u_(n)*,u_(n−1)*, . . . ,u₁*}, where u₁,u₂, . . .,u_(n)u_(n)*,u_(n−1),* . . . ,u₁* forms a conjugate and symmetricsequence, which avoids constant modulus restrictions or a limit thatantennas perform transmission by using equal powers, and can effectivelycontrol a beam shape and a beam orientation.

Further, the matrix V includes a column vector 1 and/or at least onecolumn vector v=[v₁ v₂ L v_(n) v _(n) v _(n−1) L v ₁]^(T), so thatcolumn vectors of the precoding matrix are orthogonal to each other,which can effectively reduce inter-layer interference, thereby greatlyimproving performance of MIMO, especially MU-MIMO. Therefore, theforegoing method for determining a precoding matrix can fully use adegree of freedom of controlling a beam shape and a beam orientation ofan antenna system, and meanwhile reduce inter-layer interference of MIMOtransmission as much as possible, thereby improving precision of CSIfeedback, and a system throughput.

Specifically, the base station may obtain the precoding matrix from thecodebook according to the received PMI, where the codebook is the sameas the codebook used by the user equipment. Further, the base stationmay further precode to-be-sent data according to the obtained precodingmatrix.

Using n=5 as an example, the foregoing diagonal elements u₁,u₂, . . .,u_(n), diagonal elements u_(n)*,u_(n−1)*, . . . ,u₁*, and column vectorv in this embodiment may be respectively shown in the formula (8) to theformula (12).

Using n=5 as an example, the diagonal elements μ₁,μ₂,L,μ_(n) and thediagonal elements μ_(n)*,μ_(n−1)*,L,μ₁* in the formula (5) used in thisembodiment may be respectively shown in the formula (8a) to the formula(11a).

Optionally, as another embodiment, in the matrix D, phases of thediagonal elements u₁,u₂, . . . ,u_(n) form an arithmetic progression,and phases of the diagonal elements u_(n)*,u_(n−1)*, . . . ,u₁* form anarithmetic progression. Using n=4 as an example, the diagonal elementsu₁,u₂, . . . ,u_(n) and the diagonal elements u_(n)*,u_(n−1)*, . . .,u₁* may be respectively shown in the formula (13) to the formula (16).

Using n=4 as an example, the diagonal elements μ₁,μ₂,L,μ_(n) and thediagonal elements μ_(n)*,μ_(n−1)*,L,μ₁* in the formula (5) used in thisembodiment may be respectively shown in the formula (13a) to the formula(16a).

Using n=4 as an example, the diagonal elements of the diagonal matricesshown in the formula (7) used in this embodiment may be respectivelyshown in the formula (17) to the formula (20).

In this embodiment, in the matrix D, the phases of the diagonal elementsu₁,u₂, . . . ,u_(n) form an arithmetic progression, and the phases ofthe diagonal elements u_(n)*,u_(n−1)*, . . . ,u₁* form an arithmeticprogression, which may match with an array structure of an antenna port,for example, a common uniform linear array or cross polarization array,where in the former array, array elements or antennas are arranged at asame spacing, and in the latter array, co-polarized antennas or arrayelements are arranged at a same spacing. Therefore, the phases in thearithmetic progression can improve precoding performance by using aproperty of the foregoing array structure.

Optionally, as another embodiment, the column vector v of the matrix Vmay be a column vector of a matrix [H^(T) H^(T)]^(T), where a matrix His a Hadamard matrix. Using n=4 as an example, the Hadamard matrix andthe column vector v may be respectively shown in the formula (21) to theformula (24).

In this embodiment, the column vector v is a column vector of the matrix[H^(T) H^(T)]^(T), and satisfies the property of the formula (27), andcolumn vectors of the [H^(T) H^(T)]^(T) are orthogonal to each other, sothat the obtained column vectors are orthogonal to each other, therebyreducing inter-layer interference that is generated when the precodingmatrix is used for MIMO transmission.

In this embodiment of the present invention, the determining a precodingmatrix from a codebook according to the PMI includes:

determining the precoding matrix from a codebook subset according to thePMI, where the codebook subset is a predefined codebook subset, or acodebook subset reported to the base station, or a codebook subsetreported to the base station, and returned and confirmed by the basestation. The codebook subset may be a set of the precoding matrix W=DV,where the matrix D or the matrix V is a subset of a candidate matrixthereof.

It should be understood that the precoding matrix in the codebook or thecodebook subset may be pre-stored in the user equipment and the basestation, or may be calculated by the user equipment and the base stationaccording to the structure of the foregoing precoding matrix, or may beacquired from a network device, which is not limited in the presentinvention.

The foregoing precoding matrix indicator PMI may include only one index,that is, one index directly indicates one precoding matrix, or theforegoing precoding matrix indicator may include two indexes, namely afirst index PMI1 and a second index PMI2, where the first index PMI1 andthe second index PMI2 jointly indicate the precoding matrix. Inaddition, the first index PMI1 corresponds to the matrix D. and thesecond index PMI2 corresponds to the matrix V. In an implementationmanner of this implementation manner, for precoding matrices W indicatedby two PMIs that have different first indexes PMI1 and a same secondindex PMI2, corresponding matrices D are different, and correspondingmatrices V are the same. Optionally, for precoding matrices W indicatedby two PMIs that have a same first index PMI1 and different secondindexes PMI2, corresponding matrices D are the same, and correspondingmatrices V are different.

Optionally, the foregoing first index PMI1 and second index PMI2 mayhave different time-domain granularities or frequency-domaingranularities, that is, the PMI1 and the PMI2 separately representchannel characteristics of different periods or bandwidths, or areobtained based on different subframe periods or subbands.

Optionally, as another embodiment, the base station may receive, byusing different time periods, the first index PMI1 and the second indexPMI2 that are sent by the user equipment, for example, the PMI1 may havea longer subframe period than the PMI2. In addition, the base stationmay receive, by using a PUCCH or a PUSCH, the precoding matrix indicatorPMI sent by the user equipment.

FIG. 5 is a third schematic flowchart of a specific embodiment of thepresent invention. This embodiment provides a method for determining aprecoding matrix indicator that is executed on a user equipment sidewhen a precoding matrix satisfies a first condition. As shown in FIG. 5,the method includes the following steps:

Step 501: User equipment receives a reference signal sent by a basestation.

Similar to step 301 in the embodiment shown in FIG. 3, in this step, thereference signal sent by the base station may include a CSI RS, a DM RS,or a CRS. The user equipment UE may acquire the reference signal byreceiving an eNB notification, or may obtain, based on a cell identityID, a resource configuration of the reference signal and obtain thereference signal in a corresponding resource or subframe, where the eNBnotification may be higher-layer signaling such as RRC signaling, ordynamic signaling such as DCI.

Step 502: The user equipment selects, based on the reference signal, aprecoding matrix from a codebook, where a precoding matrix W included inthe codebook is a product of a matrix W₁ and a matrix W₂, whereW=W ₁W₂  (28)

The matrix W₁ is a block diagonal matrix,W₁=diag{X₁, . . . ,X_(N) _(B) },N _(B)≥1  (29)

where at least one block matrix X is a product of a matrix D and amatrix V, and X ∈ {X₁,X₂, . . . ,X_(N) _(B) }, that is, the block matrixX has the structure shown in the formula (30):X=DV  (30 )

The matrix D is a diagonal matrix,D=α·diag{u ₁ ,u ₂ , . . . ,u _(n) U *,u _(n−1) *, . . . ,u ₁*}  (31)

where α is a complex factor, a complex number u_(i)* is a conjugatecomplex number of a complex number u_(i), and i=1, . . . ,n; and thematrix V includes a column vector 1 and/or at least one column vector v,where the column vector 1 is a column vector whose elements are all 1,and the column vector v is:V=[v ₁ v ₂ Lv _(n) v _(n) v _(n−1) Lv ₁]^(T)  (32)

where ( )^(T) represents transposition of a matrix or vector, an elementis v _(i)=−v_(i), i=1, . . . ,n, and v_(i)=±1, that is, a value of v_(i)is +1 or −1. The matrix W₂ is used to select one or more column vectorsof the matrix W₁, or is used to perform weighted combination on one ormore column vectors of the W₁ to obtain the precoding matrix W.

In another optional implementation manner of this embodiment, the blockmatrix X may be multiple different matrices, including a matrix P_(i)and a matrix P_(j), where the P_(i) and the P_(j) satisfy the formula(33):P _(i) =D(i,j)P _(j)  (33)

where the matrix D(i,j) is a diagonal matrix, and has the structureshown in the formula (5); and optionally, phases of diagonal elementsμ₁,μ₂, . . . ,μ_(n) of the matrix D(i,j) form an arithmetic progression.

Optionally, the block matrix X may be multiple different matrices,including a matrix P_(i) and a matrix P_(k), where the P_(i) and theP_(k) satisfy the formula (34):D _(i) ⁻¹ P _(i) =D _(k) ⁻¹ P _(k) =V  (34)

where the matrix V includes a column vector 1 and/or at least one columnvector v, the column vector 1 is a column vector whose elements are all1, and the column vector v has the structure shown in the formula (32);and the matrix D_(i) and the matrix D_(k) both are diagonal matrices,and have the structure shown in the formula (35):D _(m)=α·diag{u _(m,1) ,u _(m,2) , . . . ,u _(m,n) ,u _(m,n) *,u_(m,n−1) *, . . . ,u _(m,1)*},m=i,k  (35)

where α_(m) is a complex factor, and a real part or an imaginary part ofthe complex factor may be 0; a complex number u_(m,l)* is a conjugatecomplex number of a complex number u_(m,l), m=i,k, l=1, . . . , n, and nis determined by a quantity of antenna ports; and optionally, phases ofdiagonal elements u_(m,2),u_(m,2), . . . ,u_(m,n) of the matrix D_(m)form an arithmetic progression.

The user equipment may select different precoding matrices at differenttime points according to a preset rule or randomly, that is, the userequipment may determine a first precoding matrix indicator PMI at a timepoint, where the PMI corresponds to the precoding matrix P_(i) in thecodebook, and send the first PMI to the base station; and determine asecond precoding matrix indicator PMI at another time point, where thePMI corresponds to the precoding matrix D_(k) in the codebook, and sendthe second PMI to the base station.

Corresponding to the case in which the foregoing user equipment sendsthe first PMI or the second PMI at different time points, on a basestation side, the base station may also receive, at a time point, thefirst precoding matrix indicator PMI sent by the user equipment, andselect the corresponding precoding matrix P_(i) from the codebookaccording to the first PMI; and receive, at another time point, thesecond precoding matrix indicator PMI sent by the user equipment, andselect the corresponding precoding matrix D_(k) from the codebookaccording to the second PMI.

It should be pointed out that diagonal elements of the foregoingdiagonal matrix may have same amplitude. In this case, the structure ofthe foregoing precoding matrix allows that transmit antennascorresponding to rows of the precoding matrix have symmetric transmitpowers based on actual considerations, and in this case, the foregoingcodebook can still control a beam orientation by using a symmetricproperty of the powers of the transmit antennas, and meanwhile ensureorthogonality between transmission layers.

Step 503: The user equipment sends a precoding matrix indicator PMI tothe base station, where the PMI corresponds to the selected precodingmatrix.

In the foregoing embodiment of the present invention, user equipmentselects, based on a reference signal, a precoding matrix from acodebook, and sends a precoding matrix indicator PMI. A precoding matrixW included in the codebook is a product of a matrix W₁ and a matrix W₂,where the matrix W₁ is a block diagonal matrix, W₁=diag {X₁, . . .,X_(N) _(B) }, and N_(B)≥1, where at least one block matrix X is aproduct of a matrix D and a matrix V, X=DV, and X∈ {X₁,X₂, . . . ,X_(N)_(B) }. The D is a diagonal matrix and satisfies D=α·diag {u₁,u₂, . . .,u_(n),u_(n)*,u_(n−1)*, . . . ,u₁*}, where u₁,u₂, . . .,u_(n),u_(n)*,u_(n−1)*, . . . ,u₁forms a conjugate md symmetricsequence, which avoids constant modulus restrictions or a limit thatantennas perform transmission by using equal powers, and can effectivelycontrol a beam shape and a beam orientation. The matrix V includes acolumn vector 1 and/or at least one column vector v=[v₁ v₂ L v_(n) v_(n) v _(n−1) L v ₁]^(T), so that column vectors of the precoding matrixare orthogonal to each other, which can effectively reduce inter-layerinterference, thereby greatly improving performance of MIMO, especiallyMU-MIMO. Therefore, the foregoing method for determining a precodingmatrix can fully use a degree of freedom of controlling a beam shape anda beam orientation of an antenna system, and meanwhile reduceinter-layer interference of MIMO transmission as much as possible,thereby improving precision of CSI feedback, and a system throughput.

Specifically, using n=5 as an example, the foregoing diagonal elementsu₁,u₂, . . . ,u_(n), diagonal elements u_(n)*,u_(n−1)*, . . . ,u₁*, andcolumn vector v may be respectively shown in the formula (8) to theformula (12).

Using n=5 as an example, the diagonal elements μ₁,μ₂, L,μ_(n) and thediagonal elements μ_(n)*,μ_(n−1)*,L,μ₁* in the formula (5) used in thisembodiment may be respectively shown in the formula (8a) to the formula(11a).

Optionally, as another embodiment, in the matrix D, phases of thediagonal elements u₁,u₂, . . . ,u_(n) form an arithmetic progression,and phases of the diagonal elements u_(n)*,u_(n−1)*, . . . ,u₁* form anarithmetic progression. Using n=4 as an example, the diagonal elementsu₁,u₂, . . . ,u_(n) and the diagonal elements u_(n)*,u_(n−1)*, . . .,u₁* may be respectively shown in the formula (13) to the formula (16).

Using n=4 as an example, the diagonal elements μ₁,μ₂,L,μ_(n) and thediagonal elements μ_(n)*,μ_(n−1)*,L,μ₁* in the formula (5) used in thisembodiment may be respectively shown in the formula (13a) to the formula(16a).

Using n=4 as an example, the diagonal elements of the diagonal matricesin the formula (35) used in this embodiment may be respectively shown inthe formula (17) to the formula (20).

In this embodiment, in the matrix D, the phases of the diagonal elementsu₁,u₂, . . . ,u_(n) form an arithmetic progression, and the phases ofthe diagonal elements u_(n)*,u_(n−1)*, . . . ,u₁* form an arithmeticprogression, which may match with an array structure of an antenna port,for example, a common uniform linear array or cross polarization array,where in the former array, array elements or antennas are arranged at asame spacing, and in the latter array, co-polarized antennas or arrayelements are arranged at a same spacing. Therefore, the phases in thearithmetic progression can improve precoding performance by using aproperty of the foregoing array structure.

Optionally, as another embodiment, the column vector v of the matrix Vmay be a column vector of a matrix [H^(T) H^(T)]^(T), where a matrix His a Hadamard matrix. Using n=4 as an example, the Hadamard matrix andthe column vector v may be respectively shown in the formula (21) to theformula (24).

In this embodiment, the column vector v is a column vector of the matrix[H^(T) H^(T)]^(T), and satisfies the property of the formula (32), andcolumn vectors of the [H^(T) H^(T)]^(T) are orthogonal to each other, sothat the obtained column vectors are orthogonal to each other, therebyreducing inter-layer interference that is generated when the precodingmatrix is used for MIMO transmission.

In the foregoing embodiment of the present invention, the matrix W₂ isused to select a column vector of the matrix W₁, or is used to performweighted combination on a column vector of the W₁ to form the matrix W.

Using W₁=diag {X₁,X₂} as an example, where each of a block matrix X₁ anda block matrix X₂ has four columns, the W₂ may be the following matrix:

$\begin{matrix}{W_{2} \in \left\{ {{\frac{1}{\sqrt{2}}\begin{bmatrix}e_{i} \\e_{i}\end{bmatrix}},{\frac{1}{\sqrt{2}}\begin{bmatrix}e_{i} \\{je}_{i}\end{bmatrix}},{\frac{1}{\sqrt{2}}\begin{bmatrix}e_{i} \\{- e_{i}}\end{bmatrix}},{\left. {\frac{1}{\sqrt{2}}\begin{bmatrix}e_{i} \\{- {je}_{i}}\end{bmatrix}} \middle| i \right. = 1},2,3,4} \right\}} & (36)\end{matrix}$

where e_(i), i=1,2,3,4 represents a 4×1 selection vector, and exceptthat the i^(th) element is 1, other elements are all 0.

Using W₁=diag {X₁,X₂} as an example, where each of a block matrix X₁ anda block matrix X₂ has eight columns, the W₂ may be the following matrix:

$\begin{matrix}{W_{2} \in \left\{ {{\frac{1}{\sqrt{2}}\begin{bmatrix}Y \\Y\end{bmatrix}},{\frac{1}{\sqrt{2}}\begin{bmatrix}Y \\{jY}\end{bmatrix}},{\frac{1}{\sqrt{2}}\begin{bmatrix}Y \\{- Y}\end{bmatrix}},{\frac{1}{\sqrt{2}}\begin{bmatrix}Y \\{- {jY}}\end{bmatrix}}} \right\}} & (37)\end{matrix}$Y ∈{e₁,e₂,e₃,e₄,e₅,e₆,e₇,e₈}  (38)

or,

$\begin{matrix}{W_{2} \in \left\{ {{\frac{1}{2}\begin{bmatrix}Y_{1} & Y_{2} \\Y_{1} & {- Y_{2}}\end{bmatrix}},{\frac{1}{2}\begin{bmatrix}Y_{1} & Y_{2} \\{jY}_{1} & {- {jY}_{2}}\end{bmatrix}}} \right\}} & (39)\end{matrix}$(Y₁Y₂)∈{(e₁e₁),(e₂,e₂),(e₃,e₃),(e₄,e₄,),(e₁,e₂),(e₂,e₃),(e₁,e₄),(e₂,e₄)}  (40)

where e_(n), n=1,2,L,8 represents an 8×1 selection vector, and exceptthat the n^(th) element is 1, other elements are all 0.

Using W₁=diag {X₁,X₂,X₃,X₄} as an example, where each block matrix ofX₁,X₂,X₃,X₄ has four columns, the W₂ may be the following matrix:

$\begin{matrix}{W_{2} \in \left\{ {{\frac{1}{2}\begin{bmatrix}e_{i} \\{e^{j\;\theta}e_{i}} \\{e^{j\;\phi}e_{k}} \\{e^{j{({\phi + \theta})}}e_{k}}\end{bmatrix}},{\frac{1}{2}\begin{bmatrix}e_{i} \\{{- e^{j\;\theta}}e_{i}} \\{e^{j\;\phi}e_{k}} \\{{- e^{j{({\phi + \theta})}}}e_{k}}\end{bmatrix}},{\frac{1}{2}\begin{bmatrix}e_{i} \\{{je}^{j\;\theta}e_{i}} \\{e^{j\;\phi}e_{k}} \\{{je}^{j{({\phi + \theta})}}e_{k}}\end{bmatrix}},\left. {\frac{1}{2}\begin{bmatrix}e_{i} \\{{- {je}^{j\;\theta}}e_{i}} \\{e^{j\;\phi}e_{k}} \\{{- {je}^{j{({\phi + \theta})}}}e_{k}}\end{bmatrix}} \middle| \begin{matrix}{{i = 1},2,3,{4;}} \\{{k = 1},2,3,4}\end{matrix} \right.} \right\}} & (41)\end{matrix}$

where e_(i), i=1,2,3,4 represents a 4×1 selection vector, and exceptthat the i^(th) element is 1, other elements are all 0, where θ and ϕare phases, for example,

${\theta = \frac{m\;\pi}{32}},{m = 0},1,2,3,{{\ldots\mspace{14mu}{and}\mspace{14mu}\phi} = \frac{n\;\pi}{32}},{n = 0},1,2,3,{\ldots\mspace{14mu}.}$

Further, the block matrix is X₁=X₂,X₃=X₄ or X₁=X₂=X₃=X₄.

Using W₁=diag {X₁,X₂,X₃,X₄} as an example where each block matrix ofX₁,X₂,X₃,X₄ has eight columns, the W₂ may be the following matrix:

$\begin{matrix}{W_{2} \in \left\{ {{\frac{1}{2}\begin{bmatrix}Y_{1} \\{e^{j\;\theta}Y_{1}} \\{e^{j\;\phi}Y_{2}} \\{e^{j{({\phi + \theta})}}Y_{2}}\end{bmatrix}},{\frac{1}{2}\begin{bmatrix}Y_{1} \\{{- e^{j\;\theta}}Y_{1}} \\{e^{j\;\phi}Y_{2}} \\{{- e^{j{({\phi + \theta})}}}Y_{2}}\end{bmatrix}},{\frac{1}{2}\begin{bmatrix}Y_{1} \\{{je}^{j\;\theta}Y_{1}} \\{e^{j\;\phi}Y_{2}} \\{{je}^{j{({\phi + \theta})}}Y_{2}}\end{bmatrix}},{\frac{1}{2}\begin{bmatrix}Y_{1} \\{{- {je}^{j\;\theta}}Y_{1}} \\{e^{j\;\phi}Y_{2}} \\{{- {je}^{j{({\phi + \theta})}}}Y_{2}}\end{bmatrix}}} \right\}} & (42)\end{matrix}$Y₁∈{e₁,e₂,e₃,e₄,e₅,e₆,e₇,e₈}, Y₂ε{e₁,e₂,e₃,e₄,e₅,e₆,e₇,e₈}  (43)

or,

                                          (44)$W_{2} \in \begin{Bmatrix}{{\frac{1}{2\sqrt{2}}\begin{bmatrix}Y_{1,1} & Y_{1,2} \\{e^{j\;\theta}Y_{1,1}} & {e^{j\;\theta}Y_{1,2}} \\{e^{j\;\phi}Y_{2,1}} & {e^{j\;\phi}Y_{2,2}} \\{e^{j{({\phi + \theta})}}Y_{2,1}} & {e^{j{({\phi + \theta})}}Y_{2,2}}\end{bmatrix}},{\frac{1}{2\sqrt{2}}\begin{bmatrix}Y_{1,1} & Y_{1,2} \\{e^{j\;\theta}Y_{1,1}} & {{- e^{j\;\theta}}Y_{1,2}} \\{e^{j\;\phi}Y_{2,1}} & {e^{j\;\phi}Y_{2,2}} \\{e^{j{({\phi + \theta})}}Y_{2,1}} & {{- e^{j{({\phi + \theta})}}}Y_{2,2}}\end{bmatrix}},} \\{{\frac{1}{2\sqrt{2}}\begin{bmatrix}Y_{1,1} & Y_{1,2} \\{{- e^{j\;\theta}}Y_{1,1}} & {e^{j\;\theta}Y_{1,2}} \\{e^{j\;\phi}Y_{2,1}} & {e^{j\;\phi}Y_{2,2}} \\{e^{j{({\phi + \theta})}}Y_{2,1}} & {{- e^{j{({\phi + \theta})}}}Y_{2,2}}\end{bmatrix}},{\frac{1}{2\sqrt{2}}\begin{bmatrix}Y_{1,1} & Y_{1,2} \\{{- e^{j\;\theta}}Y_{1,1}} & {e^{j\;\theta}Y_{1,2}} \\{e^{j\;\phi}Y_{2,1}} & {e^{j\;\phi}Y_{2,2}} \\{{- e^{j{({\phi + \theta})}}}Y_{2,1}} & {e^{j{({\phi + \theta})}}Y_{2,2}}\end{bmatrix}}}\end{Bmatrix}$                                           (45)$\mspace{79mu}{{\left( {Y_{m,1},Y_{m,2}} \right) \in \begin{Bmatrix}{\left( {e_{1},e_{1}} \right),\left( {e_{2},e_{2}} \right),\left( {e_{3},e_{3}} \right),\left( {e_{4},e_{4}} \right),} \\{\left( {e_{1},e_{2}} \right),\left( {e_{2},e_{3}} \right),\left( {e_{1},e_{4}} \right),\left( {e_{2},e_{4}} \right)}\end{Bmatrix}},{m = 1},2}$

where e_(n),n=1,2,L,8 represents an 8×1 selection vector, and exceptthat the n^(th) element is 1, other elements are all 0, where θ and ϕare phases, for example,

${\theta = \frac{m\;\pi}{32}},{m = 0},1,2,3,{{\ldots\mspace{14mu}{and}\mspace{14mu}\phi} = \frac{n\;\pi}{32}},{n = 0},1,2,3,{\ldots\mspace{14mu}.}$

Further, the block matrix is X₁=X₂,X₃=X₄ or X₁=X₂=X₃=X₄.

In the foregoing embodiment of the present invention, the selecting, bythe user equipment based on the reference signal, a precoding matrixfrom a codebook may be specifically: obtaining, by the user equipmentbased on the reference signal, channel estimation; and selecting, basedon a predefined criterion according to the channel estimation, theprecoding matrix from the codebook, where the foregoing predefinedcriterion may be a channel capacity maximization criterion, a throughputmaximization criterion, or a cosine distance minimization criterion.

In addition, in the foregoing embodiment of the present invention, theselecting, based on the reference signal, a precoding matrix from acodebook may include: selecting the precoding matrix from a codebooksubset according to the reference signal, where the foregoing codebooksubset is a predefined codebook subset, or a codebook subset reported tothe base station, or a codebook subset reported to the base station, andreturned and confirmed by the base station; the foregoing predefinedcodebook subset may be predefined in a protocol and is known by the userequipment and the base station in the system; and the codebook subsetreported to the base station may be a codebook subset that is recentlydetermined by the user equipment and reported to the base station. Inthis embodiment, codebook subsets are set, for different applicationscenarios, in the codebook; and therefore, selecting a precoding matrixbased on a codebook subset can effectively reduce feedback overheads andthe implementation complexity.

Further, the codebook subset in the foregoing embodiment of the presentinvention may include:

a set or a precoding matrix W=V₁W₂, where W₁=diag {X₁, . . . ,X_(N) _(B)}, at least one block matrix X is a product of a matrix D and a matrixV, X ∈ {X₁,X₂, . . . ,X_(N) _(B) }, and X=DV; and the matrix D, thematrix V, or the matrix W₂ is a subset of a candidate matrix thereof.

It should be pointed out that diagonal elements of the foregoingdiagonal matrix may have same amplitude. In this case, the structure ofthe foregoing precoding matrix allows that transmit antennascorresponding to rows of the precoding matrix have symmetric transmitpowers based on actual considerations, and in this case, the foregoingcodebook can still control a beam orientation by using a symmetricproperty of the powers of the transmit antennas, and meanwhile ensureorthogonality between transmission layers.

It should be understood that the precoding matrix in the codebook or thecodebook subset may be pre-stored in the user equipment and the basestation, or may be calculated by the user equipment and the base stationaccording to the structure of the foregoing precoding matrix, or may beobtained from a network device, which is not limited in the presentinvention.

Further, in the foregoing precoding matrix, a block matrix X_(k) and ablock matrix X_(l),k≠l may be different, or may be the same. In a casein which there are multiple X_(k) s that are the same as the X_(l),k≠l,for example, the X_(k) and the X_(l),k≠l that are the same exist inpairs, feedback overheads can be further reduced. Multiple blockmatrices X_(i) in the foregoing matrix W₁ may respectively correspond toantenna port groups having different polarizations or at differentpositions, so that the foregoing precoding matrix matches with multipleantenna deployments or configurations.

In step 503 shown in the foregoing FIG. 5, the precoding matrixindicator sent to the base station may include one or more indexes.Specifically, the codebook or the codebook subset usually is a set ofone or more precoding matrices, where one precoding matrix indicatorcorresponds to one precoding matrix. Different precoding matrixindicators correspond to different precoding matrices in the codebook orthe codebook subset, and in this embodiment, the sent precoding matrixindicator corresponds to the selected precoding matrix.

Specifically, the foregoing precoding matrix indicator PMI may includeonly one index, that is, one index directly indicates one precodingmatrix, or the foregoing precoding matrix indicator may include twoindexes, namely a first index PMI1 and a second index PMI2, where thefirst index PMI1 and the second index PMI2 jointly indicate theprecoding matrix. In addition, the first index PMI1 is used forindicating the matrix W₁, and the second index PMI2 is used forindicating the matrix W₂. The foregoing first index PMI1 and secondindex PMI2 may have different time-domain granularities orfrequency-domain granularities, that is, the PMI1 and the PMI2separately represent channel characteristics of different periods orbandwidths, or are obtained based on different subframe periods orsubbands.

Optionally, the foregoing PMI may also include three indexes, where thethree indexes are respectively used for indicating the matrix D, thematrix V, and the matrix W₂.

Optionally, as another embodiment, the user equipment sends the firstindex PMI1 and the second index PMI2 to the base station by usingdifferent time periods, for example, the PMI1 may have a longer subframeperiod than the PMI2.

In addition, in step 503 in the foregoing embodiment of the presentinvention, the precoding matrix indicator information PMI may be sent tothe base station by using a PUCCH or a PUSCH.

The precoding matrix W in this embodiment may be a precoding matrixobtained by means of row or column transposition, for example, differentantenna numbers correspondingly cause row transposition of the precodingmatrix. In addition, the structure of the foregoing precoding matrix Wnot only may be used for antenna configuration in a horizontal directionin an AAS base station, but also may be used for antenna configurationin a perpendicular direction.

In this embodiment of the present invention, user equipment selects,based on a reference signal, a precoding matrix from a codebook, andsends a precoding matrix indicator PMI, where the PMI corresponds to theselected precoding matrix. A precoding matrix W included in the codebookis a product of a matrix W₁ and a matrix W₂, where the W₁ is a blockdiagonal matrix, and W₁=diag {X₁, . . . ,X_(N) _(B) }, where at leastone block matrix X is a product of a matrix D and a matrix v, X=DV, andX ∈ {X₁,X₂, . . . ,X_(N) _(B) }. The D is a diagonal matrix andsatisfies D=α·diag {u₁,u₂, . . . ,u_(n),u_(n)*,u_(n−1)*, . . . ,u₁*},where u₁,u₂, . . . ,u_(n),u_(n)*,u_(n−1)*, . . . ,u₁* forms a conjugateand symmetric sequence, which avoids constant modulus restrictions or alimit that antennas perform transmission by using equal powers, and caneffectively control a beam shape and a beam orientation. The matrix Vincludes a column vector 1 and at least one column vector v=[v₁ v₂ Lv_(n) v _(n) v _(n−1) L v ₁]^(T), so that column vectors of theprecoding matrix are orthogonal to each other, which can effectivelyreduce inter-layer interference, thereby greatly improving performanceof MIMO, especially MU-MIMO. Multiple block matrices X_(i) mayrespectively correspond to antenna port groups having differentpolarizations or at different positions, so that the foregoing precodingmatrix matches with multiple antenna deployments or configurations.Therefore, the foregoing method for determining a precoding matrix canfully use a degree of freedom of controlling a beam shape and a beamorientation in a horizontal and/or perpendicular direction of an activeantenna system, and meanwhile reduce inter-layer interference duringtransmission as much as possible, thereby improving precision of CSIfeedback, and a system throughput.

Corresponding to the embodiment shown in FIG. 5, an embodiment of thepresent invention further provides a method for determining a precodingmatrix indicator that is executed on a base station side when aprecoding matrix satisfies a first condition. FIG. 6 is a fourthschematic flowchart of a specific embodiment of the present invention.As shown in FIG. 6, the embodiment includes the following steps:

Step 601: A base station sends a reference signal to user equipment.

The foregoing sent reference signal may include multiple forms, and fordetails, reference may be made to step 501 in the embodiment shown inFIG. 5.

Step 602: The base station receives a precoding matrix indicator PMIsent by the user equipment.

Specifically, the precoding matrix indicator PMI corresponds to aprecoding matrix that is selected from a codebook by the user equipmentbased on the reference signal.

Step 603: The base station determines a precoding matrix from a codebookaccording to the PMI, where a precoding matrix W included in thecodebook is a product of a matrix W₁ and a matrix W₂, whereW=W₁ W ₂  (46)

The matrix W₁ is a block diagonal matrix,W ₁=diag{X ₁ , . . . ,X _(N) _(B) },N _(B)≥1  (47)

where at least one block matrix X is a product of a matrix D and amatrix V, and X ∈ {X₁,X₂, . . . ,X_(N) _(B) }, that is the block matrixX has the structure shown in the formula (48):X=DV  (48)

The matrix D is a diagonal matrix,D=α·diag{u ₁ ,u ₂ , . . .,u _(n) ,u _(n) *,u _(n−1) *, . . . ,u₁*}  (49)

where α is a complex factor, a complex number u_(i)* is a conjugatecomplex number of a complex number u_(i), and i=1, . . . ,n; and thematrix V includes a column vector 1 and/or at least one column vector v,where the column vector 1 is a column vector whose elements are all 1,and the column vector v is:v=[v ₁ v ₂ Lv _(n) v _(n) v _(n−1) Lv ₁]^(T)  (50)

where ( )^(T) represents transposition of a matrix or vector, an elementis v _(i)=−v_(i), i=1, . . . , n, and v_(i)=±1, that is, a value ofv_(i) is +1 or −1. The matrix W₂ is used to select one or more columnvectors of the matrix W₁, or is used to perform weighted combination onone or more column vectors of the W₁ to obtain the precoding matrix W.

In another optional implementation manner of this embodiment, the blockmatrix X may be multiple different matrices, including a matrix P_(i)and a matrix P_(j), where the P_(i) and the P_(j) satisfy the formula(51):P _(i) =D(i,j)P _(j)  (51)

where the matrix D(i,j) is a diagonal matrix, and has the structureshown in the formula (5); and optionally, phases of diagonal elementsμ₁,μ₂, . . . ,μ_(n) of the matrix D(i,j) form an arithmetic progression.

The user equipment may select different precoding matrices at differenttime points according to a preset rule or randomly, that is, the userequipment may determine a first precoding matrix indicator PMI at a timepoint, where the PMI corresponds to the precoding matrix P_(i) in thecodebook, and send the first PMI to the base station; and determine asecond precoding matrix indicator PMI at another time point, where thePMI corresponds to a precoding matrix D_(k) in the codebook, and sendthe second PMI to the base station.

Corresponding to the case in which the foregoing user equipment sendsthe first PMI or the second PMI at different time points, on a basestation side, the base station may also receive, at a time point, thefirst precoding matrix indicator PMI sent by the user equipment, andselect the corresponding precoding matrix P_(i) from the codebookaccording to the first PMI; and receive, at another time point, thesecond precoding matrix indicator PMI sent by the user equipment, andselect the corresponding precoding matrix D_(k) from the codebookaccording to the second PMI.

Optionally, the block matrix X may be multiple different matrices,including a matrix P_(i) and a matrix P_(k), where the P_(i) and theP_(k) satisfy the formula (52):D _(i) ⁻¹ P _(i) =D _(k) ⁻¹ P _(k) =V  (52)

where the matrix V includes a column vector 1 and/or at least one columnvector v, the column vector 1 is a column vector whose elements are all1, and the column vector v has the structure shown in the formula (50);and the matrix D_(i) and the matrix D_(k) both are diagonal matrices,and have the structure shown in the formula (53):D _(m)=α_(m)·diag{u _(m,1) ,u _(m,2) , . . . ,u _(m,n) ,u _(m,n) *,u_(m,n−1) *, . . . ,u _(m,1) *}m=i,k  (53)

where α_(m) is a complex factor, and a real part or an imaginary part ofthe complex factor may be 0; a complex number u_(m,l)* is a conjugatecomplex number of a complex number u_(m,l), m=i,k, l=1, . . . ,n, and nis determined by a quantity of antenna ports; and optionally, phases ofdiagonal elements u_(m,1),u_(m,2), . . . ,u_(m,n) of the matrix D_(m)form an arithmetic progression.

It should be pointed out that diagonal elements of the foregoingdiagonal matrix may have same amplitude. In this case, the structure ofthe foregoing precoding matrix allows that transmit antennascorresponding to rows of the precoding matrix have symmetric transmitpowers based on actual considerations, and in this case, the foregoingcodebook can still control a beam orientation by using a symmetricproperty of the powers of the transmit antennas, and meanwhile ensureorthogonality between transmission layers.

In the foregoing embodiment of the present invention, a base stationreceives a precoding matrix indicator PMI sent by user equipment, anddetermines a precoding matrix from a codebook according to the PMI. Aprecoding matrix W included in the codebook is a product of a matrix W₁and a matrix W₂, where the matrix W₁ is a block diagonal matrix, W₁=diag{X₁, . . . ,X_(N) _(B) }, and N_(B)≥1, where at least one block matrix Xis a product of a matrix D and a matrix V, X ∈ {X₁,X₂, . . . ,X_(N) _(B)}, and X=DV. The D is a diagonal matrix and satisfies D=α·diag {u₁,u₂, .. . ,u_(n),u_(n)*,u_(n−1)*, . . . ,u₁*}, where u₁,u₂, . . .,u_(n),u_(n)*,u_(n−1)*, . . . ,u₁* forms a conjugate and symmetricsequence, which avoids constant modulus restrictions, and caneffectively control a beam shape and a beam orientation. The matrix Vincludes a column vector 1 and at least one column vector v=[v₁ v₂ Lv_(n) v _(n) v _(n−1) L v ₁]^(T), so that column vectors of theprecoding matrix are orthogonal to each other, which can effectivelyreduce inter-layer interference, thereby greatly improving performanceof MIMO, especially MU-MIMO. Therefore, the foregoing method fordetermining a precoding matrix can fully use a degree of freedom ofcontrolling a beam shape and a beam orientation of an antenna system,and meanwhile reduce inter-layer interference of MIMO transmission asmuch as possible, thereby improving precision of CSI feedback, and asystem throughput.

Specifically, the base station may obtain the precoding matrix from thecodebook according to the received PMI, where the codebook is the sameas the codebook used by the user equipment. Further, the base stationmay further precode to-be-sent data according to the obtained precodingmatrix.

Using n=5 as an example, the foregoing diagonal elements u₁,u₂, . . .,u_(n), diagonal elements u_(n)*,u_(n−1)*, . . . ,u₁*, and column vectorv may be respectively shown in the formula (8) to the formula (12).

Using n=5 as an example, the diagonal elements μ₁,μ₂,L,μ_(n) and thediagonal elements μ_(n)*,μ_(n−1)*,L,μ₁* in the formula (5) used in thisembodiment may be respectively shown in the formula (8a) to the formula(11a).

Optionally, as another embodiment, in the matrix D, phases of thediagonal elements u₁,u₂, . . . ,u_(n) form an arithmetic progression,and phases of the diagonal elements u_(n)*,u_(n−1)*, . . . ,u₁* form anarithmetic progression. Using n=4 as an example, the diagonal elementsu₁,u₂, . . . ,u_(n) and the diagonal elements u_(n)*,u_(n−1)*, . . .,u₁* may be respectively shown in the formula (13) to the formula (16).

Using n=4 as an example, the diagonal elements μ₁,μ₂,L,μ_(n) and thediagonal elements μ_(n)*,μ_(n−1)*,L,μ₁* in the formula (5) used in thisembodiment may be respectively shown in the formula (13a) to the formula(16a).

Using n=4 as an example, the diagonal elements of the diagonal matricesshown in the formula (53) used in this embodiment may be respectivelyshown in the formula (17) to the formula (20).

In this embodiment, in the matrix D, the phases of the diagonal elementsu₁,u₂, . . . ,u_(n) form an arithmetic progression, and the phases ofthe diagonal elements u_(n)*,u_(n−1)*, . . . ,u₁* form an arithmeticprogression, which may match with an array structure of an antenna port,for example, a common uniform linear array or cross polarization array,where in the former array, array elements or antennas are arranged at asame spacing, and in the latter array, co-polarized antennas or arrayelements are arranged at a same spacing. Therefore, the phases in thearithmetic progression can improve precoding performance by using aproperty of the foregoing array structure.

Optionally, as another embodiment, the column vector v of the matrix Vmay be a column vector of a matrix [H^(T) H^(T)]^(T), where a matrix His a Hadamard matrix. Using n=4 as an example, the Hadamard matrix andthe column vector v may be respectively shown in the formula (21) to theformula (24).

In this embodiment, the column vector v is a column vector of the matrix[H^(T) H^(T)]^(T), and satisfies the property of the formula (50), andcolumn vectors of the [H^(T) H^(T)]^(T) are orthogonal to each other, sothat the obtained column vectors are orthogonal to each other, therebyreducing inter-layer interference that is generated when the precodingmatrix is used for MIMO transmission. In the foregoing embodiment of thepresent invention, the matrix W₂ is used to select a column vector ofthe matrix W₁, or is used to perform weighted combination on a columnvector of the W₁ to form the matrix W.

Using W₁=diag {X₁,X₂} an example, where each of a block matrix X₁ and ablock matrix X₂ has four columns, the W₂ may be the matrix shown in theformula (36). Using W₁=diag {X₁,X₂} as an example, where each of a blockmatrix X₁ and a block matrix X₂ has eight columns, the W₂ may be thematrix shown in the formula (37) to the formula (40).

Using W₁=diag {X₁,X₂,X₃,X₄} an example, where each block matrix ofX₁,X₂,X₃,X₄ has four columns, the W₂ may be the matrix shown in theformula (41). Further, the block matrix is X₁=X₂,X₃=X₄ or X₁=X₂=X₃=X₄.

Using W₁=diag {X₁,X₂,X₃,X₄} an example, where each block matrix ofX₁,X₂,X₃,X₄ has eight columns, the W₂ may be the matrix shown in theformula (42) to the formula (45). Further, the block matrix isX₁=X₂,X₃=X₄ or X₁=X₂=X₃=X₄.

In the foregoing embodiment of the present invention, the determining, aprecoding matrix from a codebook according to the PMI may include:

determining the precoding matrix from a codebook subset according to thePMI, where the foregoing codebook subset is a predefined codebooksubset, or a codebook subset reported to the base station, or a codebooksubset reported to the base station, and returned and confirmed by thebase station.

The foregoing codebook subset may include a set of the precoding matrixW=W₁W₂, where W₁=diag {X₁, . . . ,X_(N) _(B) }, X_(k)=DV, and the matrixD, the matrix V, or the matrix W₂ is a subset of a candidate matrixthereof.

It should be understood that the precoding matrix in the codebook or thecodebook subset may be pre-stored in the user equipment and the basestation, or may be calculated by the user equipment and the base stationaccording to the structure of the foregoing precoding matrix, which isnot limited in the present invention.

In addition, the foregoing precoding matrix indicator PMI may includeonly one index, that is, one index directly indicates one precodingmatrix, or the foregoing precoding matrix indicator may include twoindexes, namely a first index PMI1 and a second index PMI2, where thefirst index PMI1 and the second index PMI2 jointly indicate theprecoding matrix. In addition, the first index PMI1 is used forindicating the matrix W₁. and the second index PMI2 is used forindicating the matrix W₂. The foregoing first index PMI1 and secondindex PMI2 may have different time-domain granularities orfrequency-domain granularities, that is, the PMI1 and the PMI2separately represent channel characteristics of different periods orbandwidths, or are obtained based on different subframe periods orsubbands.

Optionally, the foregoing PMI may also include three indexes, where thethree indexes are respectively used for indicating the matrix D, thematrix V, and the matrix W₂.

Optionally, as another embodiment, the base station receives, by usingdifferent time periods, the first index PMI1 and the second index PMI2that are sent by the user equipment, for example, the PMI1 may have alonger subframe period than the PMI2.

Specifically, the foregoing base station may receive, by using a PUCCHor a PUSCH, the precoding matrix indicator PMI sent by the userequipment UE.

The precoding matrix W m this embodiment of the present invention may bea precoding matrix obtained by means of row or column transposition, forexample, different antenna numbers correspondingly cause rowtransposition of the precoding matrix. The precoding matrix provided inthe foregoing embodiment of the present invention not only may be usedfor antenna configuration in a horizontal direction in an AAS basestation, but also may be used for antenna configuration in aperpendicular direction.

FIG. 7 is a fifth schematic flowchart of a specific embodiment of thepresent invention. This embodiment provides a method for determining aprecoding matrix indicator that is executed on a user equipment sidewhen a precoding matrix satisfies a third condition. As shown in FIG. 7,the method includes the following steps:

Step 701: User equipment receives a reference signal sent by a basestation.

Specifically, in this step, the user equipment may receive the referencesignal in multiple manners, and the reference signal sent by the basestation may include a CSI RS, a DM RS, or a CRS. The user equipment UEmay acquire the reference signal by using a received eNB notification,or may obtain, based on a cell identity ID, a resource configuration ofthe reference signal and obtain the reference signal in a correspondingresource or subframe, where the eNB notification may be higher-layersignaling such as RRC signaling, or dynamic signaling such as DCI.

Step 702: The user equipment selects, based on the reference signal, aprecoding matrix from a codebook, where a precoding matrix W included inthe codebook is a product of a matrix W₁ and a matrix W₂, whereW=W ₁W₂  (54)

The matrix W₁ is a block diagonal matrix,W ₁=diag{X ₁ , . . . X _(N) _(B) },N _(B)≥1  (55)

where at least one block matrix X is a Kronecker product of a matrix Aand a matrix B, and X ∈ {X₁,X₂, . . . ,X_(N) _(B) }, that is, the blockmatrix X has the structure shown in the formula (56):X=A⊗B  (56)

where the matrix A or the matrix B is a product of a matrix D and amatrix V,A=DV  (57)

orB=DV  (58)

The matrix D is a diagonal matrix, and satisfies:D=α·diag{u ₁ ,u ₂ , . . . ,u _(n) ,u _(N) *,u _(n−1) *, . . . ,u₁*}  (59)

where α is a complex factor, a complex number u_(i)* is a conjugatecomplex number of a complex number u_(i), and i=1, . . . ,n; and thematrix V includes a column vector 1 and/or at least one column vector v,where the column vector 1 is a column vector whose elements are all 1,and the column vector v is:v=[v ₁ v ₂ lv _(n) v _(n) v _(n−1) Lv ₁]^(T)  (60)

where an element is v _(i)=−v_(i), i=1, . . . ,n, and v_(i)=±1, that is,a value of v_(i) is +1 or −1. The matrix W₂ is used to select one ormore column vectors of the matrix W₁, or is used to perform weightedcombination on one or more column vectors of the W₁ to obtain theprecoding matrix W.

In another optional implementation manner of this embodiment, the matrixA or the matrix B may be multiple different matrices, including a matrixP_(i) and a matrix P_(j), where the P_(i) and the P_(j) satisfy theformula (61):P _(i) =D 9 i,j)P _(j)  (61)

where the matrix D(i,j) is a diagonal matrix, and has the structureshown in the formula (5); and optionally, phases of diagonal elementsμ₁,μ₂, . . . ,μ_(n) of the matrix D(i,j) form an arithmetic progression.

Optionally, the matrix A or the matrix B may be multiple differentmatrices, including a matrix P_(i) and a matrix P_(k), where the P_(j)and the P_(k) satisfy the formula (62):D _(i) ⁻¹ P _(i) =D _(k) ⁻¹ P _(k) =V  (62)

where the matrix V includes a column vector 1 and/or at least one columnvector v, the column vector 1 is a column vector whose elements are all1, and the column vector v has the structure shown in the formula (60);and the matrix D_(i) and the matrix D_(k) both are diagonal matrices,and have the structure shown in the formula (63):D _(m)=α_(m)·diag{u _(m,1) ,u _(m,2) , . . . ,u _(m,n) ,u _(m,n) *,u_(m,n−1) *, . . . ,u _(m,1) *},m=i,k  (63)

where α_(m) is a complex factor, and a real part or an imaginary part ofthe complex factor may be 0; a complex number u_(m,l)* is a conjugatecomplex number of a complex number u_(m,l), m=i,k, l=1, . . . ,n, and nis determined by a quantity of antenna ports; and optionally, phases ofdiagonal elements u_(m,1),u_(m,2), . . . ,u_(m,n) of the matrix D_(m)form an arithmetic progression.

It should be pointed out that diagonal elements of the foregoingdiagonal matrix may have same amplitude. In this case, the structure ofthe foregoing precoding matrix allows that transmit antennascorresponding to rows of the precoding matrix have symmetric transmitpowers based on actual considerations, and in this case, the foregoingcodebook can still control a beam orientation by using a symmetricproperty of the powers of the transmit antennas, and meanwhile ensureorthogonality between transmission layers.

Step 703: The user equipment sends a precoding matrix indicator PMI tothe base station, where the PMI corresponds to the selected precodingmatrix.

In the foregoing embodiment of the present invention, user equipmentselects, based on a reference signal, a precoding matrix from acodebook, and sends a precoding matrix indicator PMI. A precoding matrixW included in the codebook is a product of a matrix W₁ and a matrix W₂,where the matrix W is a block diagonal matrix, W₁=diag {X₁, . . . ,X_(N)_(B) }, and N_(B)≥1, where at least one block matrix X is a Kroneckerproduct of a matrix A and a matrix B . X=A⊗B, and X ∈ {X₁,X₂, . . .,X_(N) _(B) }; and the matrix A or the matrix B is a product of a matrixD and a matrix V, where A=DV or B=DV. The D is a diagonal matrix andsatisfies D=α·diag {u₁,u₂, . . . ,u_(n),u_(n)*,u_(n−1)*, . . . ,u₁*},where u₁,u₂, . . . ,u_(n),u_(n)*,u_(n−1)*, . . . ,u₁* forms a conjugateand symmetric sequence, which avoids constant modulus restrictions or alimit that antennas perform transmission by using equal powers, and caneffectively control a beam shape and a beam orientation. The matrix Vincludes a column vector 1 and at least one column vector v=[v₁ v₂ Lv_(n) v _(n) v _(n−1) L v ₁]^(T), so that column vectors of theprecoding matrix are orthogonal to each other, which can effectivelyreduce inter-layer interference, thereby greatly improving performanceof MIMO, especially MU-MIMO. Therefore, the foregoing method fordetermining a precoding matrix can fully use a degree of freedom ofcontrolling a beam shape and a beam orientation in horizontal andperpendicular directions of an active antenna system, and meanwhilereduce inter-layer interference during transmission as much as possible,thereby improving precision of CSI feedback, and a system throughput.

Optionally, the base station may further obtain the precoding matrixaccording to the received PMI.

Specifically, the base station may obtain the precoding matrix from thecodebook according to the received PMI, where the codebook is the sameas the codebook used by the user equipment.

Specifically, when the matrix A is the matrix having the structure shownin the formula (57), the matrix B may be the matrix having the structureshown in the formula (58). In addition, the matrix B may also be adiscrete fourier transformation (DFT) matrix, a Householder matrix, aHadamard matrix, or a precoding matrix in a two-antenna codebook, afour-antenna codebook, or an eight-antenna codebook in an LTE R10system.

Specifically, when the matrix B is the matrix having the structure shownin the formula (57), the matrix A may be the matrix having the structureshown in the formula (58). In addition, the matrix A may also be a DFTmatrix, a Householder matrix, a Hadamard matrix, or a precoding matrixin a two-antenna codebook, a four-antenna codebook, or an eight-antennacodebook in an LTE R10 system.

Specifically, using n=5 as an example, the foregoing diagonal elementsu₁,u₂, . . . ,u_(n), diagonal elements u_(n)*,u_(n−1)*, . . . ,u₁*, andcolumn vector v may be respectively shown in the formula (8) to theformula (12).

Using n=5 as an example, the diagonal elements μ₁,μ₂,L,μ_(n) and thediagonal elements μ_(n)*,μ_(n−1)*,L,μ₁* in the formula (5) used in thisembodiment may be respectively shown in the formula (8a) to the formula(11a).

Optionally, as another embodiment, in the matrix D, phases of thediagonal elements u₁,u₂, . . . ,u_(n) form m arithmetic progression, andphases of the diagonal elements u_(n)*,u_(n−1)*, . . . ,u₁* form anarithmetic progression. Using n=4 as an example, the diagonal elementsu₁,u₂, . . . ,u_(n) and the diagonal elements u_(n)*,u_(n−1)*, . . .,u₁* may be respectively shown in the formula (13) to the formula (16).

Using n=4 as an example, the diagonal elements μ₁,μ₂,L,μ_(n) and thediagonal elements μ_(n)*,μ_(n−1)*,L,μ₁* in the formula (5) used in thisembodiment may be respectively shown in the formula (13a) to the formula(16a).

Using n=4 as an example, the diagonal elements of the diagonal matricesin the formula (63) used in this embodiment may be respectively shown inthe formula (17) to the formula (20).

In this embodiment, in the matrix D the phases of the diagonal elementsu₁,u₂, . . . ,u_(n) form an arithmetic progression, and the phases ofthe diagonal elements u_(n)*,u_(n−1)*, . . . ,u₁* form an arithmeticprogression, which may match with an array structure of an antenna port,for example, a common uniform linear array or cross polarization array,where in the former array, array elements or antennas are arranged at asame spacing, and in the latter array, co-polarized antennas or arrayelements are arranged at a same spacing. Therefore, the phases in thearithmetic progression can improve precoding performance by using aproperty of the foregoing array structure.

Optionally, as another embodiment, the column vector v of the matrix Vmay be a column vector of a matrix [H^(T) H^(T)]^(T), where a matrix His a Hadamard matrix. Using n=4 as an example, the Hadamard matrix andthe column vector v may be respectively shown in the formula (21) to theformula (24).

In this embodiment, the column vector v is a column vector of the matrix[H^(T) H^(T)]^(T), and satisfies the property of the formula (60), andcolumn vectors of the [H^(T) H^(T)]^(T) are orthogonal to each other, sothat the obtained column vectors are orthogonal to each other, therebyreducing inter-layer interference that is generated when the precodingmatrix is used for MIMO transmission.

In the foregoing embodiment of the present invention, the matrix W₂ isused to select a column vector of the matrix W₁, or is used to performweighted combination on a column vector of the W₁ to form the matrix W.

Using W₁=diag {X₁,X₂} as an example, where each of a block matrix X₁ anda block matrix X₂ has four columns, the W₂ may be the matrix shown inthe formula (36). Using W₁=diag {X₁,X₂} as an example where each of ablock matrix X₁ and a block matrix X₂ has eight columns, the W₂ may bethe matrix shown in the formula (37) to the formula (40).

Using W₁=diag {X₁,X₂,X₃,X₄} as an example where each block matrix ofX₁,X₂,X₃,X₄ has four columns, the W₂ may be the matrix shown in theformula (41). Further, the block matrix is X₁=X₂,X₃=X₄ or X₁=X₂=X₃=X₄.

Using W₁=diag {X₁,X₂,X₃,X₄} as an example, where each block matrix ofX₁,X₂,X₃,X₄ has eight columns, the W₂ may be the matrix shown in theformula (42) to the formula (45). Further, the block matrix isX₁=X₂,X₃=X₄ or X₁=X₂=X₃=X₄.

In the foregoing embodiment of the present invention, the selecting, bythe user equipment, a precoding matrix from a codebook according to thereference signal may be specifically: obtaining, by the user equipmentbased on the reference signal, channel estimation; and selecting, basedon a predefined criterion according to the channel estimation, theprecoding matrix from the codebook, where the foregoing predefinedcriterion may be a channel capacity maximization criterion, a throughputmaximization criterion, or a cosine distance minimization criterion.

In addition, in the foregoing embodiment of the present invention, theselecting a precoding matrix from a codebook according to the referencesignal may include:

selecting the precoding matrix from a codebook subset according to thereference signal, where the foregoing codebook subset is a predefinedcodebook subset, or a codebook subset reported to the base station, or acodebook subset reported to the base station, and returned and confirmedby the base station. In this embodiment, codebook subsets are set, fordifferent application scenarios, in the codebook; and therefore,selecting a precoding matrix based on a codebook subset can effectivelyreduce feedback overheads and the implementation complexity.

Specifically, the codebook subset in the foregoing embodiment of thepresent invention may include:

a set of a precoding matrix W=W₁W₂, where W₁=diag {X₁, . . . ,X_(N) _(B)}, at least one block matrix is X=A⊗B, and X ∈ {X₁,X₂, . . . ,X_(N) _(B)}, where A=DV or B=DV, and the matrix D, the matrix V, or the matrix W₂is a subset of a candidate matrix thereof.

It should be pointed out that diagonal elements of the foregoingdiagonal matrix may have same amplitude. In this case, the structure ofthe foregoing precoding matrix allows that transmit antennascorresponding to rows of the precoding matrix have symmetric transmitpowers based on actual considerations, and in this case, the foregoingcodebook can still control a beam orientation by using a symmetricproperty of the powers of the transmit antennas, and meanwhile ensureorthogonality between transmission layers.

It should be understood that the precoding matrix in the codebook or thecodebook subset may be pre-stored in the user equipment and the basestation, or may be calculated by the user equipment and the base stationaccording to the structure of the foregoing precoding matrix, which isnot limited in the present invention.

Further, in the foregoing precoding matrix, a block matrix X_(k) and ablock matrix X_(l),k≠l may different, or may be the same. In a case inwhich there are multiple X_(k) s that are the same as the X_(l),k≠l, forexample, the X_(k) and the X_(l),k≠l that are the same exist in pairs,feedback overheads can be further reduced. Multiple block matrices X_(i)in the foregoing matrix W₁ may respectively correspond to antenna portgroups having different polarizations or at different positions, so thatthe foregoing precoding matrix matches with multiple antenna deploymentsor configurations.

In step 703 shown in the foregoing FIG. 7, the precoding matrixindicator sent to the base station may include one or more indexes.Specifically, the codebook or the codebook subset usually is a set ofone or more precoding matrices, where one precoding matrix indicatorcorresponds to one precoding matrix Different precoding matrixindicators correspond to different precoding matrices in the codebook orthe codebook subset, and in this embodiment, the sent precoding matrixindicator corresponds to the selected precoding matrix.

Specifically, the foregoing precoding matrix indicator PMI may includeonly one index, that is, one index directly indicates one precodingmatrix, or the foregoing precoding matrix indicator may include twoindexes, namely a first index PMI1 and a second index PMI2, where thefirst index PMI1 and the second index PMI2 jointly indicate theprecoding matrix. In addition, the first index PMI1 is used forindicating the matrix W₁, and the second index PMI2 is used forindicating the matrix W₂. The foregoing first index PMI1 and secondindex PMI2 may have different time-domain granularities orfrequency-domain granularities, that is, the PMI1 and the PMI2separately represent channel characteristics of different periods orbandwidths, or are obtained based on different subframe periods orsubbands.

Optionally, the foregoing PMI may also include three indexes, where thethree indexes

are respectively used for indicating the matrix D, the matrix V, and thematrix W₂.

Optionally, as another embodiment, the user equipment sends the firstindex PMI1 and the second index PMI2 to the base station by usingdifferent time periods, for example, the PMI1 may have a longer subframeperiod than the PMI2.

In addition, in step 703 in the foregoing embodiment of the presentinvention, the precoding matrix indicator information PMI may be sent tothe base station by using a PUCCH or a PUSCH.

The precoding matrix W in this embodiment may be a precoding matrixobtained by means of row or column transposition, for example, differentantenna numbers correspondingly cause row transposition of the precodingmatrix. In addition, the structure of the foregoing precoding matrix Wnot only may be used for antenna configuration in a horizontal directionin an AAS base station, but also may be used for antenna configurationin a perpendicular direction.

In this embodiment of the present invention, user equipment selects,based on a reference signal, a precoding matrix from a codebook, andsends a precoding matrix indicator PMI, where the PMI corresponds to theselected precoding matrix. A precoding matrix W included in the codebookis a product of a matrix W₁ and a matrix W₂, where the W₁ is a blockdiagonal matrix, W₁=diag {X₁, . . . ,X_(N) _(B) }, and N_(B)≥1, where atleast one block matrix X is a Kronecker product of a matrix A and amatrix B , X=A⊗B, and X ∈ {X₁,X₂, . . . ,X_(N) _(B) }; and the matrix Aor the matrix B is a product of a matrix D and a matrix V. The D is adiagonal matrix and satisfies D=α·diag {u₁,u₂, . . .,u_(n),u_(n)*,u_(n−)*, . . . ,u₁*}, where u₁,u₂, . . .,u_(n),u_(n)*,u_(n−1)*, . . . ,u₁* forms a conjugate and symmetricsequence, which avoids constant modulus restrictions or a limit thatantennas perform transmission by using equal powers, and can effectivelycontrol a beam shape and a beam orientation. The matrix V includes acolumn vector 1 and at least one column vector v=[v₁ v₂ L v_(n) v _(n) v_(n−1) L v ₁]^(T), so that column vectors of the precoding matrix areorthogonal to each other, which can effectively reduce inter-layerinterference, thereby greatly improving performance of MIMO, especiallyMU-MIMO. Multiple block matrices X_(i) may respectively correspond toantenna port groups having different polarizations or at differentpositions, so that the foregoing precoding matrix matches with multipleantenna deployments or configurations. Meanwhile, the matrix A or thematrix B may separately quantize a beam in a horizontal direction and aperpendicular direction. Therefore, the foregoing method for determininga precoding matrix can fully use a degree of freedom of controlling abeam shape and a beam orientation in horizontal and perpendiculardirections of an active antenna system, and meanwhile reduce inter-layerinterference during transmission as much as possible, thereby improvingprecision of CSI feedback, and a system throughput.

Corresponding to the embodiment shown in FIG. 7, the present inventionfurther provides a method executed on a base station side. FIG. 8 is asixth schematic flowchart of a specific embodiment of the presentinvention. As shown in FIG. 8, the embodiment includes the followingsteps:

Step 801: A base station sends a reference signal to user equipment.

Specifically, for a manner in which the base station sends the referencesignal, reference may be made to step 701 shown in FIG. 7.

Step 802: Receive a precoding matrix indicator PMI sent by the userequipment.

Specifically, the precoding matrix indicator PMI corresponds to aprecoding matrix that is selected from a codebook by the user equipmentbased on the reference signal.

Step 803: Determine a precoding matrix from a codebook according to thePMI, where a precoding matrix W included in the codebook is a product ofa matrix W₁ and a matrix W₂, whereW=W₁W₂  (64)

The matrix W₁ is a block diagonal matrix,W ₁=diag{X ₁ , . . . ,X _(N) _(B) },N _(B)≥1  (65)

where at least one block matrix X is a Kronecker product of a matrix Aand a matrix B, and X ∈ {X₁,X₂, . . . ,X_(N) _(B) }, that is, the blockmatrix X has the structure shown in the formula (66):X=A⊗B  (66)

where the matrix A or the matrix B is a product of a matrix D and amatrix V,A=DV  (67)

or,B=DV  (68)

where the matrix D is a diagonal matrix, and satisfies:D=α·diag{u ₁ ,u ₂ , . . . ,u _(n) ,u _(n) *,u _(n−1) *, . . . ,u₁*}  (69)

where α is a complex factor, a complex number u_(i)* is a conjugatecomplex number of a complex number u_(i), and i=1, . . . ,n; and thematrix V includes a column vector 1 and at least one column vector v,where the column vector 1 is a column vector whose elements are all 1,and the column vector v is:v=[v ₁ v ₂ Lv _(n) v _(n) v _(n−1) Lv ₁]^(T)  (70)

where an element is v _(i)=−v_(i), i=1, . . . ,n, and v_(i)=±1, that is,a value of v_(i) is +1 or −1. The matrix W₂ is used to select one ormore column vectors of the matrix W₁, or is used to perform weightedcombination on one or more column vectors of the W₁ to obtain theprecoding matrix W.

In another optional implementation manner of this embodiment, the matrixA or the matrix B may be multiple different matrices, including a matrixP_(i) and a matrix P_(j), where the P_(i) and the P_(j) satisfy theformula (71):P _(i) D(i,j)P _(j)  (71)

where the matrix D(i,j) is a diagonal matrix, and has the structureshown in the formula (5); and optionally, phases of diagonal elementsμ₁,μ₂, . . . ,μ_(n) of the matrix D(i,j) form an arithmetic progression.

Optionally, the matrix A or the matrix B may be multiple differentmatrices, including a matrix P_(i) and a matrix P_(k), where the P_(i)and the P_(k) satisfy the formula (72):D _(i) ⁻¹ P _(i) =D _(k) ⁻¹ P _(k) =V  (72)

where the matrix V includes a column vector 1 and/or at least one columnvector v, the column vector 1 is a column vector whose elements are all1, and the column vector v has the structure shown in the formula (60);and the matrix D_(i) and the matrix D_(k) both are diagonal matrices,and have the structure shown in the formula (73):D _(m)=α_(m)·diag{u _(m,1) ,u _(m,2) , . . . ,u _(m,n) ,u _(m,n) *,u_(m,n−1) *, . . . ,u _(m,1) *},m=i,k  (73)

where α_(m) is a complex factor, and a real part or an imaginary part ofthe complex factor may be 0; a complex number u_(m,l)* is a conjugatecomplex number of a complex number u_(m,l), m=i,k, l=1, . . . ,n, and nis determined by a quantity of antenna ports; and optionally, phases ofdiagonal elements u_(m,1),u_(m,2), . . . ,u_(m,n) of the matrix D_(m)form an arithmetic progression.

It should be pointed out that diagonal elements of the foregoingdiagonal matrix may have same amplitude. In this case, the structure ofthe foregoing precoding matrix allows that transmit antennascorresponding to rows of the precoding matrix have symmetric transmitpowers based on actual considerations, and in this case, the foregoingcodebook can still control a beam orientation by using a symmetricproperty of the powers of the transmit antennas, and meanwhile ensureorthogonality between transmission layers.

In the foregoing embodiment of the present invention, a base stationreceives a precoding matrix indicator PMI sent by user equipment, anddetermines a precoding matrix from a codebook according to the PMI. Aprecoding matrix W included in the codebook is a product of a matrix W₁and a matrix W₂, where the matrix W₁ is a block diagonal matrix, W₁=diag{X₁, . . . ,X_(N) _(B) }, and N_(B)≥1, where at least one block matrix Xis a Kronecker product of a matrix A and a matrix B, X=A⊗B, and X ∈{X₁,X₂, . . . ,X_(N) _(B) }; and the matrix A or the matrix B is aproduct of a matrix D and a matrix V, where A=DV or B=DV. The D is adiagonal matrix and satisfies D=α·diag {u₁,u₂, . . .,u_(n),u_(n)*,u_(n−1)*, . . . ,u₁*}, where u₁,u₂, . . .,u_(n),u_(n)*,u_(n−1), . . . ,u₁* forms a conjugate and symmetricsequence, which avoids constant modulus restrictions or a limit thatantennas perform transmission by using equal powers, and can effectivelycontrol a beam shape and a beam orientation. The matrix V includes acolumn vector 1 and at least one column vector v=[v₁ v₂ L v_(n) v _(n) v_(n−1) L v ₁]^(T), so that column vectors of the precoding matrix areorthogonal to each other, which can effectively reduce inter-layerinterference, thereby greatly improving performance of MIMO, especiallyMU-MIMO. Therefore, the foregoing method for determining a precodingmatrix can fully use a degree of freedom of controlling a beam shape anda beam orientation in horizontal and perpendicular directions of anactive antenna system, and meanwhile reduce inter-layer interferenceduring transmission as much as possible, thereby improving precision ofCSI feedback, and a system throughput.

Specifically, the base station may obtain the precoding matrix from thecodebook according to the received PMI, where the codebook is the sameas the codebook used by the user equipment. Further, the base stationmay further precode to-be-sent data according to the obtained precodingmatrix.

Specifically, when the matrix A is the matrix having the structure shownin the formula (67), the matrix B may be the matrix having the structureshown in the formula (68). The matrix B may also be a DFT matrix, aHouseholder matrix, a Hadamard matrix, or a precoding matrix in atwo-antenna codebook, a four-antenna codebook, or an eight-antennacodebook in an LTE R10 system.

Specifically, when the matrix B is the matrix having the structure shownin the formula (68), the matrix A may be the matrix having the structureshown in the formula (67). The matrix A may also be a DFT matrix, aHouseholder matrix, a Hadamard matrix, or a precoding matrix in atwo-antenna codebook, a four-antenna codebook, or an eight-antennacodebook in an LTE R10 system.

Specifically, using n=5 as an example, the foregoing diagonal elementsu₁u₂, . . . ,u_(n), diagonal elements u_(n)*,u_(n−1)*, . . . ,u₁*, andcolumn vector v may be respectively shown in the formula (8) to theformula (12).

Using n=5 as an example, the diagonal elements μ₁,μ₂,L,μ_(n) and thediagonal elements μ_(n)*,μ_(n−1)*,L,μ₁* in the formula (5) used in thisembodiment may be respectively shown in the formula (8a) to the formula(11a).

Optionally, as another embodiment, in the matrix D, phases of thediagonal elements u₁,u₂, . . . ,u_(n) form an arithmetic progression,and phases of the diagonal elements u_(n)*,u_(n−1)*, . . . ,u₁* form anarithmetic progression.

Using n−4 as an example, the diagonal elements u₁,u₂, . . . ,u_(n) andthe diagonal elements u_(n)*,u_(n−1), . . . ,u₁* may be respectivelyshown in the formula (13) to the formula (16).

Using n=4 as an example, the diagonal elements μ₁,μ₂,L,μ_(n) and thediagonal elements μ_(n)*,μ_(n−1)*,Lμ₁* in the formula (5) used in thisembodiment may be respectively shown in the formula (13a) to the formula(16a).

Using n=4 as an example, the diagonal elements of the diagonal matricesin the formula (73) used in this embodiment may be respectively shown inthe formula (17) to the formula (20).

In this embodiment, in the matrix D, the phases of the diagonal elementsu₁,u₂, . . . ,u_(n) form an arithmetic progression, and the phases ofthe diagonal elements u_(n)*,u_(n−1)*, . . . ,u₁* form an arithmeticprogression, which may match with an array structure of an antenna port,for example, a common uniform linear array or cross polarization array,where in the former array, array elements or antennas are arranged at asame spacing, and in the latter array, co-polarized antennas or arrayelements are arranged at a same spacing. Therefore, the phases in thearithmetic progression can improve precoding performance by using aproperty of the foregoing array structure.

Optionally, as another embodiment, the column vector v of the matrix Vmay be a column vector of a matrix [H^(T) H^(T)]^(T), where a matrix His a Hadamard matrix. Using n=4 as an example, the Hadamard matrix andthe column vector v may be respectively shown in the formula (21) to theformula (24).

In this embodiment, the column vector v is a column vector of the matrix[H^(T) H^(T)]^(T), and satisfies the property of the formula (70), andcolumn vectors of the [H^(T) H^(T)]^(T) are orthogonal to each other, sothat the obtained column vectors are orthogonal to each other, therebyreducing inter-layer interference that is generated when the precodingmatrix is used for MIMO transmission.

In the foregoing embodiment of the present invention, the matrix W₂ isused to select a column vector of the matrix W₁, or is used to performweighted combination on a column vector of the W₁ to form the matrix W.Using W₁=diag {X₁,X₂} as an example where each of a block matrix X₁ anda block matrix X₂ has four columns, the W₂ may be the matrix shown inthe formula (36). Using W₁=diag {X₁,X₂} as an example where each of ablock matrix X₁ and a block matrix X₂ has eight columns, the W₂ may bethe matrix shown in the formula (37) to the formula (40).

Using W₁=diag {X₁,X₂,X₃,X₄} as an example where each block matrix ofX₁,X₂,X₃,X₄ has four columns, the W₂ may be the matrix shown in theformula (41). Further, the block matrix is X₁=X₂,X₃=X₄ or X₁=X₂=X₃=X₄.

Using W₁=diag {X₁,X₂,X₃,X₄} as an example where each block matrix ofX₁,X₂, X₃,X₄ has eight columns, the W₂ may be the matrix shown in theformula (42) to the formula (45). Further, the block matrix isX₁=X₂,X₃=X₄ or X₁=X₂=X₃=X₄.

In the foregoing embodiment of the present invention, the determining aprecoding matrix from a codebook according to the PMI includes:

determining the precoding matrix from the codebook according to the PMI,where the foregoing codebook subset is a predefined codebook subset, ora codebook subset reported to the base station, or a codebook subsetreported to the base station, and returned and confirmed by the basestation. In this embodiment, codebook subsets are set, for differentapplication scenarios, in the codebook; and therefore, selecting aprecoding matrix based on a codebook subset can effectively reducefeedback overheads and the implementation complexity.

Specifically, the codebook subset in the foregoing embodiment of thepresent invention may include:

a set or a precoding matrix W=W₁W₂, where W₁=diag {X₁, . . . ,X_(N) _(B)}, at least one block matrix is X=A⊗B, and X ∈ {X₁,X₂, . . . ,X_(N) _(B)}, where A=DV or B=DV, and the matrix D, the matrix V, or the matrix W₂is a subset of a candidate matrix thereof.

It should be pointed out that diagonal elements of the foregoingdiagonal matrix may have same amplitude. In this case, the structure ofthe foregoing precoding matrix allows that transmit antennascorresponding to rows of the precoding matrix have symmetric transmitpowers based on actual considerations, and in this case, the foregoingcodebook can still control a beam orientation by using a symmetricproperty of the powers of the transmit antennas, and meanwhile ensureorthogonality between transmission layers.

It should be understood that the precoding matrix in the codebook or thecodebook subset may be pre-stored in the user equipment and the basestation, or may be calculated by the user equipment and the base stationaccording to the structure of the foregoing precoding matrix, which isnot limited in the present invention.

In addition, the precoding matrix indicator sent to the base station mayinclude one or more indexes. Specifically, the codebook or the codebooksubset usually is a set of one or more precoding matrices, where oneprecoding matrix indicator corresponds to one precoding matrix.Different precoding matrix indicators correspond to different precodingmatrices in the codebook or the codebook subset, and in this embodiment,the sent precoding matrix indicator corresponds to the selectedprecoding matrix.

Specifically, the foregoing precoding matrix indicator PMI may includeonly one index, that is, one index directly indicates one precodingmatrix, or the foregoing precoding matrix indicator may include twoindexes, namely a first index PMI1 and a second index PMI2, where thefirst index PMI1 and the second index PMI2 jointly indicate theprecoding matrix. In addition, the first index PMI1 is used forindicating the matrix W₁, and the second index PMI2 is used forindicating the matrix W₂. The foregoing first index PMI1 and secondindex PMI2 may have different time-domain granularities orfrequency-domain granularities, that is, the PMI1 and the PMI2separately represent channel characteristics of different periods orbandwidths, or are obtained based on different subframe periods orsubbands.

Optionally, the foregoing PMI may also include three indexes, where thethree indexes are respectively used for indicating the matrix D, thematrix V, and the matrix W₂.

Optionally, as another embodiment, the base station receives, by usingdifferent time periods, the first index PMI1 and the second index PMI2that are sent by the user equipment, for example, the PMI1 may have alonger subframe period than the PMI2.

Specifically, the foregoing base station may receive, by using a PUCCHor a PUSCH, the precoding matrix indicator PMI sent by the userequipment UE.

The precoding matrix W m this embodiment of the present invention may bea precoding matrix obtained by means of row or column transposition, forexample, different antenna numbers correspondingly cause rowtransposition of the precoding matrix.

In the foregoing embodiment of the present invention, a base stationsends a reference signal and receives a precoding matrix indicator PMIsent by user equipment, where the PMI corresponds to a precoding matrixthat is selected from a codebook by the user equipment based on thereference signal. A precoding matrix W included in the codebook is aproduct of a matrix W₁ and a matrix W₂, where the W₁ is a block diagonalmatrix, W₁=diag {W₁, . . . ,X_(N) _(B) }, and N_(B)≥1, where at leastone block matrix X is a Kronecker product of a matrix A and a matrix B,X=A⊗B, and X ∈ {X₁,X₂, . . . ,X_(N) _(B) }; and the matrix A or thematrix B is a product of a matrix D and a matrix V. The D is a diagonalmatrix and satisfies D=α·diag {u₁,u₂, . . . ,u_(m),u_(n)*,u_(n−1)*, . .. ,u₁*}, where u₁,u₂, . . . ,u_(n),u_(n)*,u_(n−1)*, . . . ,u₁* forms aconjugate and symmetric sequence, which avoids constant modulusrestrictions, and can effectively control a beam shape and a beamorientation. The matrix V includes a column vector 1 and at least onecolumn vector v=[v₁ v₂ L v_(n) v _(n) v _(n−1) L v ₁]^(T), so thatcolumn vectors of the precoding matrix are orthogonal to each other,which can effectively reduce inter-layer interference, thereby greatlyimproving performance of MIMO, especially MU-MIMO. Therefore, theforegoing method for determining a precoding matrix can fully use adegree of freedom of controlling a beam shape and a beam orientation inhorizontal and perpendicular directions of an active antenna system, andmeanwhile reduce inter-layer interference during transmission as much aspossible, thereby improving precision of CSI feedback, and a systemthroughput.

FIG. 9 is a first schematic structural diagram of an apparatus fordetermining a precoding matrix indicator according to an embodiment ofthe present invention. As shown in FIG. 9, the apparatus includes afirst determining module 11 and a first sending module 12. The firstdetermining module is configured to determine a precoding matrixindicator PMI, where the PMI corresponds to a precoding matrix and theprecoding matrix W satisfies a first condition, a second condition, or athird condition; and

the first sending module is configured to send the PMI to a basestation, where

the first condition is that the precoding matrix W satisfies W=DV, wherethe matrix D is a diagonal matrix, D=α·diag {u₁,u₂, . . .,u_(n),u_(n)*,u_(n−1)*, . . . ,u₁*}, α is a complex factor, a complexnumber u_(i)* is a conjugate complex number of a complex number μ_(i),and n is determined by a quantity of antenna ports; and the matrix V isa constant modulus matrix;

the second condition is that the precoding matrix W includes one or morecolumn vectors of a block diagonal matrix W₁, or the precoding matrix Wis obtained by performing weighted combination on one or more columnvectors of a block diagonal matrix W₁, where W₁=diag {X₁, . . . ,X_(N)_(B) }, and N_(B)≥1, where at least one block matrix X is a product X=DVof a matrix D and a matrix V, and X ∈ {X₁,X₂, . . . ,X_(N) _(B) }; thematrix D is a diagonal matrix, D=α·diag {u₁,u₂, . . .,u_(n),u_(n)*,u_(n−1)*, . . . ,u₁*}, α is a complex factor, a complexnumber u_(i)* is a conjugate complex number of a complex number u_(i),and n is determined by a quantity of antenna ports; and the matrix V isa constant modulus matrix; and

the third condition is that the precoding matrix W includes one or morecolumn vectors of a block diagonal matrix W₁, or the precoding matrix Wis obtained by performing weighted combination on one or more columnvectors of a block diagonal matrix W₁, where W₁=diag {X₁, . . . ,X_(N)_(B) }, and N_(B)≥1, where at least one block matrix X is a Kroneckerproduct of a matrix A and a matrix B, X=A⊗B, and X ∈ {X₁,X₂, . . .,X_(N) _(B) }; the matrix A or the matrix B is a product of a matrix Dand a matrix V; the matrix D is a diagonal matrix, D=α·diag {u₁,u₂, . .. ,u_(n),u_(n)*,u_(n−1)*, . . . ,u₁*}, α is a complex factor, a complexnumber u_(i)* is a conjugate complex number of a complex number u_(i),i=1, . . .,n, and n is a quantity of rows of the matrix A or the matrixB; and the matrix V is a constant modulus matrix.

In the second condition or the third condition, the precoding matrix Wsatisfies W=W₁W₂, where the matrix W₂ is used to select one or morecolumn vectors of the matrix W₁; or is used to perform weightedcombination on one or more column vectors of the W₁ to obtain theprecoding matrix W.

Phases of diagonal elements u₁,u₂, . . . ,u_(n) of the foregoing matrixD form an arithmetic progression.

The foregoing matrix V includes a column vector 1 and/or at least onecolumn vector v, the column vector 1 is a column vector whose elementsare all 1, and the column vector v is v=[v₁ v₂₁ L v_(n) v _(n) v _(n−1)L v ₁]^(T), where an element is v _(i)=−v_(i),v_(i)=±1, and i=1, . . .,n. The matrix V includes only the column vector 1 and the at least onecolumn vector v, and when the matrix V includes multiple column vectorsv, the multiple column vectors v are different. Optionally, the columnvector v of the matrix V is a column vector of a matrix [H^(T)H^(T)]^(T), where a matrix H is a Hadamard matrix.

In addition, the foregoing PMI includes a first index PMI1 and a secondindex PMI2, where

when the precoding matrix W satisfies the first condition, the firstindex PMI1 corresponds to the matrix D, and the second index PMI2corresponds to the matrix V;

when the precoding matrix W satisfies the second condition, the firstindex PMI1 corresponds to the matrix W₁, and the second index PMI2corresponds to the matrix W₂; or

when the precoding matrix W satisfies the third condition, the firstindex PMI1 corresponds to the matrix W₁, and the second index PMI2corresponds to the matrix W₂. Further, the foregoing first index PMI1and second index PMI2 have different time-domain granularities orfrequency-domain granularities; or the first index PMI1 and the secondindex PMI2 are sent to the base station by using different time periods.

In the foregoing embodiment of the present invention, the foregoingapparatus further includes:

a first receiving module, configured to receive a reference signal sentby the base station, and select, from a codebook according to thereference signal, the precoding matrix W corresponding to the PMI.

The codebook includes a precoding matrix W_(i) and a precoding matrixW_(j), and the two precoding matrices satisfy W_(i)=D(i,j)W_(j), whereD(i,j)=α_((i,j))diag {μ₁,μ₂, . . . ,μ_(n),μ_(n)*,μ_(n−1)*, . . . ,μ₁*},α_((i,j)) is a complex factor a complex number μ_(m)* is a conjugatecomplex number of a complex number μ_(m), m=1, . . . ,n, and n isdetermined by a quantity of antenna ports. Optionally, phases ofdiagonal elements μ₁,μ₂, . . . ,μ_(n) of the foregoing matrix D(i,j)form an arithmetic progression.

Alternatively, the foregoing codebook includes a precoding matrix w_(i)and a precoding matrix W_(k), and the two precoding matrices satisfyD_(i) ⁻¹W_(i)=D_(k) ⁻¹W_(k)=V, where D_(m)=α_(m)·diag {u_(m,1),u_(m,2),. . . ,u_(m,n),u_(m,n)*,u_(m,n−1)*, . . . ,u_(m,1)*}, m=i,k, α_(m) is acomplex factor, a complex number u_(m,l)* is a conjugate complex numberof a complex number u_(m,l), m=i,k, l=1, . . . ,n, and n is determinedby a quantity of antenna ports.

Optionally, phases of diagonal elements u_(m,1),u_(m,2), . . . ,u_(m,n)of the matrix D_(m) form an arithmetic progression.

FIG. 10 is a second schematic structural diagram of an apparatus fordetermining a precoding matrix indicator according to an embodiment ofthe present invention. As shown in FIG. 10, the apparatus includes asecond receiving module 21 and a second determining module 22. Thesecond receiving module 21 is configured to receive a precoding matrixindicator PMI sent by user equipment; and the second determining module22 is configured to determine a corresponding precoding matrix Waccording to the PMI, where the precoding matrix W satisfies a firstcondition, a second condition, or a third condition, where the firstcondition is that the precoding matrix W satisfies W=DV; the secondcondition is that the precoding matrix W includes one or more columnvectors of a block diagonal matrix W₁, or the precoding matrix W isobtained by performing weighted combination on one or more columnvectors of a block diagonal matrix W₁, where W₁=diag {X₁, . . . ,X_(N)_(B) }, and N_(B)≥1, where at least one block matrix X is a product X=DVof a matrix D and a matrix V, and X ∈ {X₁,X₂, . . . ,X_(N) _(B) }; andthe third condition is that the precoding matrix W includes one or morecolumn vectors of a block diagonal matrix W₁, or the precoding matrix Wis obtained by performing weighted combination on one or more columnvectors of a block diagonal matrix W₁, where W₁=diag {X₁, . . . ,X_(N)_(B) }, and N_(B)≥1, where at least one block matrix X is a Kroneckerproduct of a matrix A and a matrix B, X=A⊗B, and X ∈ {X₁,X₂, . . .,X_(N) _(B) }; the matrix A or the matrix B is a product of a matrix Dand a matrix V; the matrix D is a diagonal matrix, i=1, . . . ,n, and nis a quantity of rows of the matrix A or the matrix B, where

the matrix D is a diagonal matrix, D=α·diag {u₁,u₂, . . .,u_(n),u_(n)*u_(n−1)*, . . . ,u₁*}, α is a complex factor, a complexnumber u_(i)* is a conjugate complex number of a complex number u_(i),and n is determined by a quantity of antenna ports; and the matrix V isa constant modulus matrix.

In the foregoing embodiment of the present invention, in the secondcondition or the third condition, the precoding matrix W satisfiesW=W₁W₂, where the matrix W₂ is used to select one or more column vectorsof the matrix W₁; or is used to perform weighted combination on one ormore column vectors of the W₁ to obtain the precoding matrix W.

Optionally, phases of diagonal elements u₁,u₂, . . . ,u_(n) of theforegoing matrix D form an arithmetic progression.

Further, the matrix V includes a column vector 1 and/or at least onecolumn vector v, the column vector 1 is a column vector whose elementsare all 1, and the column vector v is v=[v₁ v₂ L v_(n) v _(n) v _(n−1) Lv ₁]^(T), where an element is v _(i)=−v_(i),v_(i)=±1, and i=1, . . . ,n.Optionally, the matrix V includes only the column vector 1 and the atleast one column vector v, and when the matrix V includes multiplecolumn vectors v, the multiple column vectors v are different.

In addition, the column vector v of the foregoing matrix V is a columnvector of a matrix [H^(T) H^(T)]^(T), where a matrix H is a Hadamardmatrix.

In the foregoing embodiment of the present invention, the precodingmatrix indicator PMI includes a first index PMI1 and a second indexPMI2, where

when the precoding matrix W satisfies the first condition, the firstindex PMI1 corresponds to the matrix D, and the second index PMI2corresponds to the matrix V;

when the precoding matrix W satisfies the second condition, the firstindex PMI1 corresponds to the matrix W₁, and the second index PMI2corresponds to the matrix W₂; or

when the precoding matrix W satisfies the third condition, the firstindex PMI1 corresponds to the matrix W₁, and the second index PMI2corresponds to the matrix W₂.

Optionally, the first index PMI1 and the second index PMI2 havedifferent time-domain granularities or frequency-domain granularities;or the first index PMI1 and the second index PMI2 are sent to the basestation by using different time periods.

In addition, the foregoing determining a corresponding precoding matrixW according to the PMI includes:

selecting the corresponding precoding matrix W from a codebook accordingto the PMI.

Specifically, the foregoing codebook includes a precoding matrix W_(i)and a precoding matrix W_(j), and the two precoding matrices satisfyW_(i)=D(i,j)W_(j), where D(i,j)=α_((i,j))diag {ρ₁,μ₂, . . .,μ_(n),μ_(n)*,μ_(n−1)*, . . . ,μ₁*}, α_((i,j)) is a complex factor acomplex number μ_(m)* is a conjugate complex number of a complex numberμ_(m), n=1, . . . ,n, and n is determined by a quantity of antennaports.

Phases of diagonal elements μ₁,μ₂, . . . ,μ_(n) of the matrix D(i,j)form an arithmetic progression.

Alternatively, the foregoing codebook includes a precoding matrix W_(i)and a precoding matrix W_(k), and the two precoding matrices satisfyD_(i) ⁻¹W_(i)=D_(k) ⁻¹W_(k)=V, where D_(m)=α_(m)·diag {u_(m,1),u_(m,2),. . . ,u_(m,n),u_(m,n)*,u_(m,n−1)*, . . . ,u_(m,1)*}, m=i,k, α_(m) is acomplex factor, a complex number u_(m,l)* is a conjugate complex numberof a complex number u_(m,l), m=i,k, l=1, . . . ,n, and n is determinedby a quantity of antenna ports.

Phases of diagonal elements u_(m,1),u_(m,2), . . . ,u_(m,n) of theforegoing matrix D_(m) form an arithmetic progression.

FIG. 11 is a third schematic structural diagram of an apparatus fordetermining a precoding matrix indicator according to an embodiment ofthe present invention. As shown in FIG. 11, the apparatus includes athird determining module 31 and a second sending module 32. The thirddetermining module 31 is configured to determine a first precodingmatrix indicator PMI, where the PMI corresponds to a precoding matrixW_(i) in a codebook; and the second sending module 32 is configured tosend the first PMI to a base station, where the codebook includes atleast: the precoding matrix W_(i) and a precoding matrix W_(j), and theprecoding matrix W_(i) and the precoding matrix W_(j) in the codebooksatisfy W_(i)=D(i,j)W_(j), where D(i,j)=α_((i,j))diag {μ₁,μ₂, . . .,μ_(n),μ_(n)*,μ_(n−1)*, . . . ,μ₁*}, α_((i,j)) is a complex factor acomplex number μ_(m)* is a conjugate complex number of a complex numberμ_(m), m=1, . . . ,n, and n is determined by a quantity of antennaports.

Optionally, phases of diagonal elements μ₁,μ₂, . . . ,μ_(n) of theforegoing matrix D(i,j) form an arithmetic progression.

FIG. 12 is a fourth schematic structural diagram of an apparatus fordetermining a precoding matrix indicator according to an embodiment ofthe present invention. As shown in FIG. 12, the apparatus includes athird receiving module 41 and a fourth determining module 42. The thirdreceiving module 41 is configured to receive a first precoding matrixindicator PMI sent by user equipment; and the fourth determining module42 is configured to determine a corresponding precoding matrix W_(i)from a codebook according to the first PMI, where the codebook includesat least: the precoding matrix W_(i) and a precoding matrix W_(j), andthe precoding matrix W_(i) and the precoding matrix W_(j) in thecodebook satisfy W_(i)=D(i,j)W_(j), where D(i,j)=α_((i,j))·diag {μ₁,μ₂,. . . ,μ_(n),μ_(m)*,μ_(n−1)*, . . . ,μ₁*}, α_((i,j)) is a complex factora complex number μ_(m)* is a conjugate complex number of a complexnumber μ_(m), m=1, . . . ,n, and n is determined by a quantity ofantenna ports.

Optionally, phases of diagonal elements μ₁,μ₂, . . . ,μ_(n) of theforegoing matrix D(i,j) form an arithmetic progression.

FIG. 13 is a fifth schematic structural diagram of an apparatus fordetermining a precoding matrix indicator according to an embodiment ofthe present invention. As shown in FIG. 13, the apparatus includes afifth determining module 51 and a third sending module 52. The fifthdetermining module 51 is configured to determine a first precodingmatrix indicator PMI, where the first PMI corresponds to a precodingmatrix W_(i) in a codebook; and the third sending module 52 isconfigured to send the first PMI to a base station, where the codebookincludes at least: the precoding matrix W_(i) and a precoding matrixW_(j), and the precoding matrix W_(i) and a precoding matrix W_(k) inthe codebook satisfy D_(i) ⁻¹W_(i)=D_(k) ⁻¹W_(k)=V, whereD_(m)=α_(m)·diag {u_(m,1)u_(m,2), . . . ,u_(m,n)u_(m,n)*,u_(m,n−1)*, . .. ,u_(m,1)*}, m=i,k, α_(m) is a complex factor, a complex numberu_(m,l)* is a conjugate complex number of a complex number u_(m,l),m=i,k, l=1, . . . ,n, and n is determined by a quantity of antennaports; and the matrix V is a constant modulus matrix.

Optionally, phases of diagonal elements u_(m,1),u_(m,2), . . . ,u_(m,n)of the foregoing matrix D_(m) form an arithmetic progression.

FIG. 14 is a sixth schematic structural diagram of an apparatus fordetermining a precoding matrix indicator according to an embodiment ofthe present invention.

As shown in FIG. 14, the apparatus includes a fourth receiving module 61and a sixth determining module 62. The fourth receiving module 61 isconfigured to receive a first precoding matrix indicator PMI sent byuser equipment; and the sixth determining module 62 is configured todetermine a corresponding precoding matrix W_(i) from a codebookaccording to the first PMI, where the codebook includes at least: theprecoding matrix W_(i) and a precoding matrix W_(j), and the precodingmatrix W_(i) and a precoding matrix W_(k) in the codebook satisfy D_(i)⁻¹W_(i)=D_(k) ⁻¹W_(k)=V, where D_(m)=α_(m)·diag {u_(m,1),u_(m,2), . . .,u_(m,n),u_(m,n)*,u_(m,n−1)*, . . . ,u_(m,1)*}, m=i,k, α_(m) is acomplex factor, a complex number u_(m,l)* is a conjugate complex numberof a complex number u_(m,l), m=i,k, l=1, . . . ,n, and n is determinedby a quantity of antenna ports; and the matrix V is a constant modulusmatrix.

Optionally, phases of diagonal elements u_(m,1),u_(m,2). . . ,u_(m,n) ofthe foregoing matrix D_(m) form an arithmetic progression.

FIG. 15 is a first schematic structural diagram of user equipmentaccording to an embodiment of the present invention. As shown in FIG.14, the user equipment includes a first processor 71 and a firsttransmitter 72. The first processor 71 is configured to determine aprecoding matrix indicator PMI, where the PMI corresponds to a precodingmatrix W, and the precoding matrix W satisfies a first condition, asecond condition, or a third condition; and the first transmitter 72 isconfigured to send the PMI to a base station, where the first conditionis that the precoding matrix W satisfies W=DV, where the matrix D is adiagonal matrix, D=α·diag {u₁,u₂, . . . ,u_(n),u_(n)*,u_(n−1)*, . . .,u₁*}, α is a complex factor, a complex number u_(i)* is a conjugatecomplex number of a complex number u_(i), and n is determined by aquantity of antenna ports; and the matrix V is a constant modulusmatrix; the second condition is that the precoding matrix W includes oneor more column vectors of a block diagonal matrix W₁, or the precodingmatrix W is obtained by performing weighted combination on one or morecolumn vectors of a block diagonal matrix W₁, where W₁=diag {X₁, . . .,X_(N) _(B) }, and N_(B)≥1, where at least one block matrix X is aproduct X=DV of a matrix D and a matrix V, and X ∈ {X₁,X₂, . . . ,X_(N)_(B) }; the matrix D is a diagonal matrix, D=α·diag {u₁,u₂, . . .,u_(n),u_(n)*,u_(n−1)*, . . . ,u₁*}, α is a complex factor, a complexnumber u_(i)* is a conjugate complex number of a complex number u_(i),and n is determined by a quantity of antenna ports; and the matrix V isa constant modulus matrix; and the third condition is that the precodingmatrix W includes one or more column vectors of a block diagonal matrixW₁, or the precoding matrix W is obtained by performing weightedcombination on one or more column vectors of a block diagonal matrix W₁,where W₁=diag {X₁, . . . ,X_(N) _(B) }, and N_(B)≥1, where at least oneblock matrix X is a Kronecker product of a matrix A and a matrix B,X=A⊗B, and X ∈ {X₁,X₂, . . . ,X_(N) _(B) }; the matrix A or the matrix Bis a product of a matrix D and a matrix V; the matrix D is a diagonalmatrix, D=α·diag {u₁,u₂, . . . ,u_(n)u_(n)*,u_(n−1)*, . . . ,u₁*}, α isa complex factor, a complex number u_(i)* is a conjugate complex numberof a complex number u_(i), i=1, . . . ,n, and n is a quantity of rows ofthe matrix A or the matrix B; and the matrix V is a constant modulusmatrix.

In the foregoing embodiment of the present invention, in the secondcondition or the third condition, the precoding matrix W satisfiesW=W₁W₂, where the matrix W₂ is used to select one or more column vectorsof the matrix W₁; or is used to perform weighted combination on one ormore column vectors of the W₁ to obtain the precoding matrix W.

Optionally, phases of diagonal elements u₁,u₂, . . . ,u_(n) of theforegoing matrix D form an arithmetic progression.

In addition, the matrix V includes a column vector 1 and/or at least onecolumn vector v, the column vector 1 is a column vector whose elementsare all 1, and the column vector v is v=[v₁ v₂ L v_(n) v _(n) v _(n−1) Lv ₁]^(T), where and element is v _(i)=−v_(i),v₁=±1, and i=1, . . . ,n.Optionally, the matrix V includes only the column vector 1 and the atleast one column vector v, and when the matrix V includes multiplecolumn vectors v, the multiple column vectors v are different. Thecolumn vector v of the foregoing matrix V is a column vector of a matrix[H^(T) H^(T)]^(T), where a matrix H is a Hadamard matrix.

In the foregoing embodiment of the present invention, the PMI includes afirst index PMI1 and a second index PMI2, where

when the precoding matrix W satisfies the first condition, the firstindex PMI1 corresponds to the matrix D, and the second index PMI2corresponds to the matrix V;

when the precoding matrix W satisfies the second condition, the firstindex PMI1 corresponds to the matrix W₁, and the second index PMI2corresponds to the matrix W₂; or

when the precoding matrix W satisfies the third condition, the firstindex PMI1 corresponds to the matrix W₁, and the second index PMI2corresponds to the matrix W₂.

Optionally, the foregoing first index PMI1 and second index PMI2 havedifferent time-domain granularities or frequency-domain granularities;or the first index PMI1 and the second index PMI2 are sent to the basestation by using different time periods.

In the foregoing embodiment of the present invention, the user equipmentfurther includes:

a first receiver, configured to receive a reference signal sent by thebase station, and select, from a codebook according to the referencesignal, the precoding matrix W corresponding to the PMI.

The foregoing codebook includes the precoding matrix W₁ and a precodingmatrix W_(j), and the two precoding matrices satisfy W_(i)=D(i,j)W_(j),where D(i,j)=α_((i,j))diag {μ₁,μ₂, . . . ,μ_(n),μ_(n)*,μ_(n−1)*, . . .,μ₁*}, α_((i,j)) is a complex factor a complex number μ_(n)* is aconjugate complex number of a complex number μ_(m), m=1, . . . ,n, and nis determined by a quantity of antenna ports.

Optionally, phases of diagonal elements μ₁,μ₂, . . . ,μ_(n) of thematrix D(i,j) form an arithmetic progression.

Alternatively, the foregoing codebook includes the precoding matrixW_(i) and a precoding matrix W_(k), and the two precoding matricessatisfy D_(i) ⁻¹W_(i)=D_(k) ⁻¹W_(k)=V, where D_(m)=α_(m)·diag{u_(m,1),u_(m,2), . . . ,u_(m,n),u_(m,n)*,u_(m,n−1), . . . ,u_(m,1)*},m=i,k, α_(m) is a complex factor, a complex number u_(m,l)* is aconjugate complex number of a complex number u_(m,l), m=i,k, l=1, . . .,n, and n is determined by a quantity of antenna ports.

Optionally, phases of diagonal elements u_(m,1),u_(m,2), . . . ,u_(m,n)of the foregoing matrix D_(m) form an arithmetic progression.

FIG. 16 is a first schematic structural diagram of a base stationaccording to an embodiment of the present invention. As shown in FIG.16, the base station includes a second receiver 81 and a secondprocessor 82. The second receiver 81 is configured to receive aprecoding matrix indicator PMI sent by user equipment; and the secondprocessor 82 is configured to determine a corresponding precoding matrixW according to the PMI, where the precoding matrix W satisfies a firstcondition, a second condition, or a third condition, where

the first condition is that the precoding matrix W satisfies W=DV;

the second condition is that the precoding matrix W includes one or morecolumn vectors of a block diagonal matrix W₁, or the precoding matrix Wis obtained by performing weighted combination on one or more columnvectors of a block diagonal matrix W₁, where W₁=diag {X₁, . . . ,X_(N)_(B) }, and N_(B)≥1, where at least one block matrix X is a product X=DVof a matrix D and a matrix V, and X ∈ {X₁,X₂, . . . ,X_(N) _(B) }; and

the third condition is that the precoding matrix W includes one or morecolumn vectors of a block diagonal matrix W₁, or the precoding matrix Wis obtained by performing weighted combination on one or more columnvectors of a block diagonal matrix W₁, where W₁=diag {X₁, . . . ,X_(N)_(B) }, and N_(B)≥1, where at least one block matrix X is a Kroneckerproduct of a matrix A and a matrix B, X=A⊗B, and X ∈ {X₁,X₂, . . .,X_(N) _(B) }; the matrix A or the matrix B is a product of a matrix Dand a matrix V; the matrix D is a diagonal matrix, i=1, . . . , n, and nis a quantity of rows of the matrix A or the matrix B, where

the matrix D is a diagonal matrix, D=α·diag {u₁,u₂, . . .,u_(n),u_(n)*,u_(n−1)*, . . . ,u₁*}, α is a complex factor, a complexnumber u_(i)* is a conjugate complex number of a complex number u_(i),and n is determined by a quantity of antenna ports; and the matrix V isa constant modulus matrix.

In the foregoing embodiment of the present invention, in the secondcondition or the third condition, the precoding matrix W satisfiesW=W₁W₂, where the matrix W₂ is used to select one or more column vectorsof the matrix W₁; or is used to perform weighted combination on one ormore column vectors of the W₁ to obtain the precoding matrix W.

Optionally, phases of diagonal elements u₁,u₂, . . . ,u_(n) of thematrix D form an arithmetic progression.

In the foregoing embodiment of the present invention, the matrix Vincludes a column vector 1 and/or at least one column vector v, thecolumn vector 1 is a column vector whose elements are all 1, and thecolumn vector v is v=[v₁ v₂ L v_(n) v _(n) v _(n−1) L v ₁]^(T), where anelement is v _(i)=−v_(i),v_(i=±)1, and i=1, . . . ,n. Optionally, thematrix V includes only the column vector 1 and the at least one columnvector v, and when the matrix V includes multiple column vectors v, themultiple column vectors v are different. In addition, the column vectorv of the foregoing matrix V is a column vector of a matrix [H^(T)H^(T)]^(T), where a matrix H is a Hadamard matrix.

In the foregoing embodiment of the present invention, the precodingmatrix indicator PMI includes a first index PMI1 and a second indexPMI2, where when the precoding matrix W satisfies the first condition,the first index PMI1 corresponds to the matrix D, and the second indexPMI2 corresponds to the matrix V; when the precoding matrix W satisfiesthe second condition, the first index PMI1 corresponds to the matrix andthe second index PMI2 corresponds to the matrix W₂; or when theprecoding matrix W satisfies the third condition, the first index PMI1corresponds to the matrix W₁, and the second index PMI2 corresponds tothe matrix W₂.

Optionally, the first index PMI1 and the second index PMI2 havedifferent time-domain granularities or frequency-domain granularities;or the first index PMI1 and the second index PMI2 are sent to the basestation by using different time periods.

In the foregoing embodiment of the present invention, the determining acorresponding precoding matrix W according to the PMI includes:

selecting the corresponding precoding matrix W from a codebook accordingto the PMI.

In addition, the foregoing codebook includes a precoding matrix W_(j)and a precoding matrix W_(j), and the two precoding matrices satisfyW_(i)=D(i,j)W_(j), where D(i,j)=α_((i,j))diag {μ₁,μ₂, . . .,μ_(n),μ_(n)*,μ_(n−1)*, . . . ,μ₁*}, α_((i,j)) is a complex factor, acomplex number μ_(m)* is a conjugate complex number of a complex numberμ_(m), m=1, . . . ,n, and n is determined by a quantity of antennaports. Optionally, phases of diagonal elements μ₁,μ₂, . . . ,μ_(n) ofthe matrix D(i,j) form an arithmetic progression.

Alternatively, the codebook includes a precoding matrix W_(i) and aprecoding matrix W_(k), and the two precoding matrices satisfy D_(i)⁻¹W_(i)=D_(k) ⁻¹W_(k)=V, where D_(m)=α_(m)·diag {u_(m,1),u_(m,2), . . .,u_(m,n),u_(m,n)*,u_(m,n−1)*, . . . ,u_(m,1)*}, m=i,k, α_(m) is acomplex factor, a complex number u_(m,l)* is a conjugate complex numberof a complex number u_(m,l), m=i,k, i=1, . . . ,n, and n is determinedby a quantity of antenna ports. Optionally, phases of diagonal elementsu_(m,1),u_(m,2), . . . ,u_(m,n) of the foregoing matrix D_(m) form anarithmetic progression.

FIG. 17 is a second schematic structural diagram of user equipmentaccording to an embodiment of the present invention. As shown in FIG.17, the user equipment includes a third processor 73 and a secondtransmitter 74. The third processor 73 is configured to determine afirst precoding matrix indicator PMI, where the PMI corresponds to aprecoding matrix W_(i) in a codebook; and the second transmitter 74 isconfigured to send the first PMI to a base station, where

the codebook includes at least: the precoding matrix W_(i) and aprecoding matrix W_(j), and the precoding matrix W_(i) and the precodingmatrix W_(j) in the codebook satisfy W_(i)=D(i,j)W_(j), whereD(i,j)=α_((i,j))diag {μ₁,μ₂,. . . ,μ_(n),μ_(n)*,μ_(n−1)*, . . . ,μ₁*},α_((i,j)) is a complex factor, a complex number μ_(m)* is a conjugatecomplex number of a complex number μ_(m), m=1, . . . ,n, and n isdetermined by a quantity of antenna ports.

Optionally, phases of diagonal elements μ₁,μ₂, . . . ,μ_(n) of theforegoing matrix D(i,j) form an arithmetic progression.

FIG. 18 is a second schematic structural diagram of a base stationaccording to an embodiment of the present invention. As shown in FIG.18, the base station includes a third receiver 81 and a fourth processor82. The third receiver 81 included in the base station is configured toreceive a first precoding matrix indicator PMI sent by user equipment;and the fourth processor 82 is configured to determine a correspondingprecoding matrix W_(i) from a codebook according to the first PMI, wherethe codebook includes at least: the precoding matrix W_(i) and aprecoding matrix W_(j), and the precoding matrix W_(i) and the precodingmatrix W_(j) in the codebook satisfy W_(i)=D(i,j)W_(j), whereD(i,j)=α_((i,j))diag {μ₁,μ₂, . . . ,μ_(n),μ_(n)*, μ_(n−1)*, . . . ,μ₁*},α_((i,j)) is a complex factor, a complex number μ_(m)* is a conjugatecomplex number of a complex number μ_(m), m=1, . . . ,n, and n isdetermined by a quantity of antenna ports.

Optionally, phases of diagonal elements μ₁,μ₂, . . . ,μ_(n) of theforegoing matrix D(i,j) form an arithmetic progression.

FIG. 19 is a third schematic structural diagram of user equipmentaccording to an embodiment of the present invention. As shown in FIG.19, the user equipment includes a fifth processor 75 and a thirdtransmitter 76. The fifth processor 75 is configured to determine afirst precoding matrix indicator PMI, where the first PMI corresponds toa precoding matrix W_(i) in a codebook; and the third transmitter 76 isconfigured to send the first PMI to a base station, where the codebookincludes at least: the precoding matrix W_(i) and a precoding matrixW_(j), and the precoding matrix W_(i) and a precoding matrix W_(k) inthe codebook satisfy D_(i) ⁻¹W_(i)=D_(k) ⁻¹W_(k)=V, whereD_(m)=α_(m)·diag {u_(m,1),u_(m,2), . . . ,u_(m,n),u_(m,n)*,u_(m,n−1)*, .. . ,u_(m,1)*}, m=i,l, α_(m) is a complex factor, a complex numberu_(m,l)* is a conjugate complex number of a complex number u_(m,l),m=i,k, l=1, . . . ,n, and n is determined by a quantity of antennaports; and the matrix V is a constant modulus matrix.

Optionally, phases of diagonal elements u_(m,1),u_(m,2), . . . ,u_(m,n)of the foregoing matrix D_(m) form an arithmetic progression.

FIG. 20 is a third schematic structural diagram of a base stationaccording to an embodiment of the present invention. As shown in FIG.20, the base station includes a fourth receiver 85 and a sixth processor86. The fourth receiver 85 is configured to receive a first precodingmatrix indicator PMI sent by user equipment; and the sixth processor 86is configured to determine a corresponding precoding matrix W_(i) from acodebook according to the first PMI, where the codebook includes atleast: the precoding matrix W_(i) and a precoding matrix W_(j), and theprecoding matrix W_(i) and a precoding matrix W_(k) in the codebooksatisfy D_(i) ⁻¹W_(i)=D_(k) ⁻¹W_(k)=V, where D_(m)=α_(m)·diag{u_(m,1),u_(m,2), . . . ,u_(m,n),u_(m,n)*,u_(m,n−1)*, . . . ,u_(m,1)*},m=i,k, α_(m) is a complex factor, a complex number u_(m,l)* is aconjugate complex number of a complex number u_(m,l), m=i,k, l=1, . . .,n, and n is determined by a quantity of antenna ports; and the matrix Vis a constant modulus matrix.

Optionally, phases of diagonal elements u_(m,1),u_(m,2), . . . ,u_(m,n)of the foregoing matrix D_(m) form an arithmetic progression.

A person of ordinary skill in the art may understand that all or some ofthe steps of the method embodiments may be implemented by a programinstructing relevant hardware. The program may be stored in acomputer-readable storage medium. When the program runs, the steps ofthe method embodiments are performed. The foregoing storage mediumincludes: any medium that can store program code, such as a ROM, a RAM,a magnetic disk, or an optical disc.

Finally, it should be noted that the foregoing embodiments are merelyintended for describing the technical solutions of the presentinvention, but not for limiting the present invention. Although thepresent invention is described in detail with reference to the foregoingembodiments, persons of ordinary skill in the art should understand thatthey may still make modifications to the technical solutions describedin the foregoing embodiments or make equivalent replacements to some orall technical features thereof, without departing from the scope of thetechnical solutions of the embodiments of the present invention.

The invention claimed is:
 1. A method for determining a precoding matrixindicator (PMI), comprising: receiving, by a user equipment, a referencesignal sent by a base station; and determining, by the user equipment,the PMI according to the reference signal, wherein the PMI correspondsto a precoding matrix W, and the precoding matrix W satisfies: theprecoding matrix W comprises one or more column vectors of a blockdiagonal matrix W₁, or the precoding matrix W is obtained by performingweighted combination on one or more column vectors of a block diagonalmatrix W₁, wherein W₁=diag{X₁, . . . ,X_(N) _(B) }, and N_(B)≥1, whereinat least one block matrix X is a Kronecker product of a matrix A and amatrix B, X=A⊗B, and X ∈ {X₁,X₂, . . . ,X_(N) _(B) }; the matrix A orthe matrix B is a product of a matrix D and a matrix V; the matrix D isa diagonal matrix, D=α·diag{u₁,u₂, . . . ,u_(n),u_(n)*,u_(n−1)*, . . .,u₁*}, α is a complex factor, a complex number u_(i)* is a conjugatecomplex number of a complex number u_(i), i=1, . . . ,n, and n is aquantity of rows of the matrix A or the matrix B; and the matrix V is aconstant modulus matrix; wherein the precoding matrix W satisfiesW=W₁W₂, wherein the matrix W₂ is used to select one or more columnvectors of the matrix W₁; or is used to perform weighted combination onone or more column vectors of the W₁ to obtain the precoding matrix W;and sending, by the user equipment, the PMI to the base station.
 2. Themethod according to claim 1, wherein phases of diagonal elements u₁, u₂,. . . ,u_(n) of the matrix D form an arithmetic progression.
 3. Themethod according to claim 1, wherein the matrix V comprises at least oneof a column vector 1 and one or more column vectors vm, the columnvector 1 is a column vector whose elements are all 1, and any columnvector vm is in the form v=[v₁ v₂ L v_(n) v _(n) v _(n−1) L v ₁]^(T),wherein an element is v _(i)=−v_(i),v_(i)=±1, i=1, . . . ,n i=1, . . .,n, and [ ]^(T) denotes a transposing matrix.
 4. The method according toclaim 1, wherein the precoding matrix W is used to control a beam shapeand a beam orientation, in a horizontal direction and a perpendiculardirection.
 5. A method for determining a precoding matrix indicator(PMI), comprising: transmitting, by a base station, a reference signalto a user equipment; receiving, by the base station, the PMI, accordingto the reference signal, and sent by the user equipment; determining, bythe base station, a corresponding precoding matrix W according to thePMI, wherein the precoding matrix W satisfies: the precoding matrix Wcomprises one or more column vectors of a block diagonal matrix W₁, orthe precoding matrix W is obtained by performing weighted combination onone or more column vectors of a block diagonal matrix W₁, whereinW₁=diag {X₁, . . . ,X_(N) _(B) }, and N_(B)≥1, wherein at least oneblock matrix X is a Kronecker product of a matrix A and a matrix B,X=A⊗B, and X∈ {X₁,X₂, . . . ,X_(N) _(B) }; the matrix A or the matrix Bis a product of a matrix D and a matrix V, the matrix D is a diagonalmatrix, i=1, . . . ,n, and n is a quantity of rows of the matrix A orthe matrix B , wherein the matrix D is a diagonal matrix, D=α·diag{u₁,u₂, . . . ,u_(n),u_(n)*,u_(n−1)*, . . . ,u₁*}, α is a complexfactor, a complex number u_(i)* is a conjugate complex number of acomplex number u_(i), and n is determined by a quantity of antennaports; and the matrix V is a constant modulus matrix; wherein theprecoding matrix W satisfies W=W₁W₂, wherein the matrix W₂ is used toselect one or more column vectors of the matrix W₁; or is used toperform weighted combination on one or more column vectors of the W₁ toobtain the precoding matrix W.
 6. The method according to claim 5,wherein phases of diagonal elements u₁,u₂, . . . ,u_(n) of the matrix Dform an arithmetic progression.
 7. The method according to claim 5,wherein the matrix V comprises at least one of a column vector 1 and oneor more column vectors vm, the column vector 1 is a column vector whoseelements are all 1, and any column vector vm is in the form v=[v₁ v₂ Lv_(n) v _(n) v _(n−1) L v ₁]^(T), wherein an element is v_(i)=−v_(i),v_(i)=±1, i=1, . . . ,n i=1, . . . ,n, and [ ]^(T) denotes atransposing matrix.
 8. A user equipment, comprising: a receiver,configured to receive a reference signal sent by a base station; a firstprocessor, configured to determine a precoding matrix indicator (PMI)according to the reference signal, wherein the PMI corresponds to aprecoding matrix W, and the precoding matrix W satisfies the precodingmatrix W comprises one or more column vectors of a block diagonal matrixW₁, or the precoding matrix W is obtained by performing weightedcombination on one or more column vectors of a block diagonal matrix W₁,wherein W₁=diag {X₁, . . . ,X_(N) _(B) }, wherein at least one blockmatrix X is a Kronecker product of a matrix A and a matrix B, X=A⊗B, andX∈ {X₁,X₂, . . . ,X_(N) _(B) }; the matrix A or the matrix B is aproduct of a matrix D and a matrix V; the matrix D is a diagonal matrix,D=α·diag {u₁,u₂, . . . ,u_(n),u_(n)*,u_(n−1)*, . . . ,u₁*}, α is acomplex factor, a complex number u_(i)* is a conjugate complex number ofa complex number u_(i), i=1, . . . ,n, and n is a quantity of rows ofthe matrix A or the matrix B ; and the matrix V is a constant modulusmatrix; wherein the precoding matrix W satisfies W=W₁W₂, wherein thematrix W₂ is used to select one or more column vectors of the matrix W₁;or is used to perform weighted combination on one or more column vectorsof the W₁ to obtain the precoding matrix W; and a first transmitter,configured to send the PMI to the base station to be used by the basestation.
 9. The user equipment according to claim 8, wherein phases ofdiagonal elements u₁,u₂, . . . ,u_(n) of the matrix D form an arithmeticprogression.
 10. The user equipment according to claim 8, wherein thematrix V comprises at least one of a column vector 1 and one or morecolumn vectors vm, the column vector 1 is a column vector whose elementsare all 1, and any column vector vm is in the form v=[v₁ v₂ L v_(n) v_(n) v _(n−1) L v ₁]^(T), wherein an element is v _(i)=−v_(i),v_(i)=±1,i=1, . . . ,n i=1, . . . ,n, and [ ]^(T) denotes a transporting matrix.11. Abase station, comprising: a transmitter, configured to transmit areference signal to a user equipment; a receiver, configured to receivea precoding matrix indicator PMI according to the reference signal, andsent by the user equipment; and a second processor, configured to:determine a corresponding precoding matrix W according to the PMI,wherein the precoding matrix W comprises one or more column vectors of ablock diagonal matrix W₁, or the precoding matrix W is obtained byperforming weighted combination on one or more column vectors of a blockdiagonal matrix W₁, wherein W₁=diag {X₁, . . . ,X_(N) _(B) }, andN_(B)≥1, wherein at least one block matrix X is a Kronecker product of amatrix A and a matrix B, X=A⊗B, and X∈ {X₁,X₂, . . . ,X_(N) _(B) }; thematrix A or the matrix B is a product of a matrix D and a matrix V; thematrix D is a diagonal matrix, i=1, . . . ,n, and n is a quantity ofrows of the matrix A or the matrix B, wherein the matrix D is a diagonalmatrix, D=α·diag {u₁,u₂, . . . ,u_(n),u_(n)*,u_(n−1)*, . . . ,u₁*}, α isa complex factor, a complex number u_(i)* is a conjugate complex numberof a complex number u_(i), and n is determined by a quantity of antennaports; and the matrix V is a constant modulus matrix; wherein theprecoding matrix W satisfies W=W₁W₂, wherein the matrix W₂ is used toselect one or more column vectors of the matrix W₁; or is used toperform weighted combination on one or more column vectors of the W₁ toobtain the precoding matrix W.
 12. The base station according to claim11, wherein phases of diagonal elements u₁,u₂, . . . ,u_(n) of thematrix D form an arithmetic progression.
 13. The base station accordingto claim 11, wherein the matrix V comprises at least one of a columnvector 1 and one or more column vectors vm, the column vector 1 is acolumn vector whose elements are all 1, and any column vector vm is inthe form v=[v₁ v₂ L v_(n) v _(n) v _(n−1) L v ₁]^(T), wherein an elementis v _(i)=−v_(i),v_(i)=±1, i=1, . . . ,n i=1, . . . ,n, and [ ]^(T)denotes a transporting matrix.